See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/320932767 Scaling biodiversity responses to hydrological regimes Article in Biological Reviews · November 2017 DOI: 10.1111/brv.12381 CITATIONS 2 READS 637 7 authors, including: Some of the authors of this publication are also working on these related projects: Stream conservation and forest management View project Cross-ecosystems subsidies, trophic organization and ecosystem functioning in high-latitude streams View project Rob Rolls University of Canberra 23 PUBLICATIONS 310 CITATIONS SEE PROFILE Jani Heino Finnish Environment Institute 175 PUBLICATIONS 5,780 CITATIONS SEE PROFILE Bruce Chessman Chessman Ecology 112 PUBLICATIONS 3,287 CITATIONS SEE PROFILE Ross M Thompson University of Canberra 156 PUBLICATIONS 3,358 CITATIONS SEE PROFILE All content following this page was uploaded by Rob Rolls on 12 April 2018. The user has requested enhancement of the downloaded file.
Biol. Rev. (2018), 93, pp. 971–995. 971doi: 10.1111/brv.12381
Scaling biodiversity responses to hydrologicalregimes
Robert J. Rolls1,2∗ , Jani Heino3, Darren S. Ryder2, Bruce C. Chessman4,Ivor O. Growns2, Ross M. Thompson1 and Keith B. Gido5
1Institute for Applied Ecology, University of Canberra, Canberra ACT 2601, Australia2School of Environmental and Rural Science, University of New England, Armidale, New South Wales 2351, Australia3Finnish Environment Institute, Natural Environment Centre, Biodiversity, Oulu, Finland47 Dalrymple Crescent, Pymble, New South Wales 2073, Australia5Division of Biology, Kansas State University, Manhattan, KS, U.S.A.
ABSTRACT
Of all ecosystems, freshwaters support the most dynamic and highly concentrated biodiversity on Earth. These attributesof freshwater biodiversity along with increasing demand for water mean that these systems serve as significant models tounderstand drivers of global biodiversity change. Freshwater biodiversity changes are often attributed to hydrologicalalteration by water-resource development and climate change owing to the role of the hydrological regime of rivers,wetlands and floodplains affecting patterns of biodiversity. However, a major gap remains in conceptualising how thehydrological regime determines patterns in biodiversity’s multiple spatial components and facets (taxonomic, functionaland phylogenetic). We synthesised primary evidence of freshwater biodiversity responses to natural hydrological regimesto determine how distinct ecohydrological mechanisms affect freshwater biodiversity at local, landscape and regionalspatial scales. Hydrological connectivity influences local and landscape biodiversity, yet responses vary dependingon spatial scale. Biodiversity at local scales is generally positively associated with increasing connectivity whereaslandscape-scale biodiversity is greater with increasing fragmentation among locations. The effects of hydrologicaldisturbance on freshwater biodiversity are variable at separate spatial scales and depend on disturbance frequencyand history and organism characteristics. The role of hydrology in determining habitat for freshwater biodiversityalso depends on spatial scaling. At local scales, persistence, stability and size of habitat each contribute to patternsof freshwater biodiversity yet the responses are variable across the organism groups that constitute overall freshwaterbiodiversity. We present a conceptual model to unite the effects of different ecohydrological mechanisms on freshwaterbiodiversity across spatial scales, and develop four principles for applying a multi-scaled understanding of freshwaterbiodiversity responses to hydrological regimes. The protection and restoration of freshwater biodiversity is both afundamental justification and a central goal of environmental water allocation worldwide. Clearer integration ofconcepts of spatial scaling in the context of understanding impacts of hydrological regimes on biodiversity willincrease uptake of evidence into environmental flow implementation, identify suitable biodiversity targets responsive tohydrological change or restoration, and identify and manage risks of environmental flows contributing to biodiversitydecline.
Key words: biotic homogenisation, climate change, community composition, diversity, drought, environmental flows,flow regulation, spatial scaling, species richness.
(1) Effects of hydrological connectivity on freshwater biodiversity across spatial scales . . . . . . . . . . . . . . . . . . . 977(2) Effects of hydrological disturbance on freshwater biodiversity across spatial scales . . . . . . . . . . . . . . . . . . . 980(3) Effects of hydrological habitat gradients on freshwater biodiversity across spatial scales . . . . . . . . . . . . . . 981
V. A conceptual model of the hydrological drivers of multi-scaled freshwater biodiversity . . . . . . . . . . . . . . . . . . 982VI. Principles and applications of a multi-scaled conceptual understanding of freshwater biodiversity responses
for quantifying the true impacts of hydrological change on freshwater biodiversity . . . . . . . . . . . . . . . . . . . 984(2) Principle 2: effects of hydrological change on freshwater biodiversity are best addressed when the
specific spatial scale(s) of impact and underlying ecohydrological mechanisms are identified . . . . . . . . . 985(3) Principle 3: risks of environmental flows as a driver of further biodiversity decline can be addressed
The hydrological regime plays a central role in thebiophysical dynamics of freshwater environments, such asrivers, floodplains, and wetlands (Hart & Finelli, 1999;Sponseller, Heffernan & Fisher, 2013). Understanding theresponses of freshwater biodiversity to hydrological variationis key to predicting the consequences of changing hydrologydue to human water use and climate change. Specifically,these mechanistic relationships are key to informing themanagement of hydrological regimes to protect or restorefreshwater biodiversity and ecosystem services (Davies et al.,2014). However, ambiguous and inconsistent relationshipsbetween hydrology and freshwater biodiversity have beenreported (Dewson, James & Death, 2007; Downes, 2010).In part, this inconsistency is likely because research hasinadequately distinguished how effects of hydrology onfreshwater biodiversity vary across spatial scales (Pegg &Taylor, 2007) or condense biodiversity to simple metrics withno reference to spatial scaling (e.g. Yang, Sun & Yang, 2016).Consequently, there remains a clear need to determine themechanisms underlying effects of hydrology on freshwaterbiodiversity across spatial scales. A strengthened conceptualunderstanding of the relationships between hydrology andbiodiversity across spatial scales would be of significant
value to global efforts to manage hydrological regimes forbiodiversity outcomes.
Conceptual models of linkages between hydrology andfreshwater biodiversity vary in the extent to which theyincorporate the role of ecohydrological mechanisms acrossspatial scales (Lake, 2000; Ward & Tockner, 2001; Larnedet al., 2010). Existing models have a strong focus onthe effects of distinct components of the hydrologicalregime. Both Lake (2000) and Lepori & Hjerdt (2006), forexample, emphasise the role of hydrological disturbances(e.g. floods) as drivers of temporal variation in speciesdiversity. By contrast, Ward, Tockner & Schiemer (1999)and Larned et al. (2010) focus on the role of aquatic habitatpatch size and among-patch connectivity in response towater-level fluctuations influencing the number of taxaoccupying patches and variation in assemblage compositionamong patches at the scale of individual rivers and theirfloodplains. These existing conceptualisations therefore focuson the role of individual ecohydrological mechanisms (sensu
Sponseller et al., 2013) in isolation and do not integratehow spatial dynamics of biodiversity vary in responseto hydrological regimes. This limitation highlights that asignificant gap remains in understanding how hydrologicalregimes influence freshwater biodiversity from individualpatches to across multiple regions.
Table 1. Definition of terms used in this synthesis relevant to conceptualising the effects of hydrological regimes on multi-scalebiodiversity patterns in freshwater ecosystems
Term Definition
Biodiversity The variability among living organisms from all sources, inter alia, terrestrial, marine and other aquaticecosystems and the ecological complexes of which they are a part; this includes variation within species,among species and of ecosystems [Convention on Biological Diversity (Gaston, 1996)]
Taxonomic diversity (TD) The variety and variation of organisms based on taxonomy measured at multiple spatial scales. Also knownas species diversity (where species-level taxonomy is used to discriminate organisms)
Functional diversity (FD) The breadth of biological or functional characteristics of organisms within a community, measured atmultiple spatial scales (Petchey & Gaston, 2006). Often referred to as functional composition or traitdiversity
Phylogenetic diversity (PD) The breadth of evolutionary history among organisms in a community (Faith, 1992; Graham & Fine,2008). Phylogenetic diversity emphasises the phylogenetic distinctness of organisms, and therefore futureevolutionary potential
Alpha diversity The number of taxa (TD), number of functional characteristics (FD), or the breadth of phylogeneticdistinctness among taxa (PD) within a location. Forms part of ‘inventory diversity’ (Jurasinski, Retzer &Beierkuhnlein, 2009)
Gamma diversity The number of taxa (TD), number of functional characteristics (FD), or the breadth of phylogeneticdistinctness among taxa (PD) within a region. Forms part of ‘inventory diversity’ (Jurasinski et al., 2009)
Beta diversity Spatial variation in the composition of taxa, functional groups or phylogenies among locations within aregion (Anderson et al., 2011). Beta diversity is most commonly considered with respect to taxonomicdiversity, yet is also applied to functional and phylogenetic diversity (e.g. Graham & Fine, 2008; Villeger,Grenouillet & Brosse, 2013). Beta diversity occurs via two processes: turnover (replacement) andnestedness (loss) (Baselga, 2010; Legendre, 2014). Described as ‘differentiation diversity’ (Jurasinski et al.,2009)
Biotic homogenisation The process of increasing similarity of communities (taxonomic, functional or phylogenetic) over time(Olden & Rooney, 2006). Quantified by declines in beta diversity and driven by species invasions,extinctions, and environmental changes
Spatial scale Spatial scale has two core components: spatial grain and spatial extent. Spatial grain refers to the size of theindividual sample unit considered in a study, whereas spatial extent is the overall area covered by a study,and hence contains all sampling units (Wiens, 1989; Whittaker, Willis & Field, 2001)
Location A location refers to the study site and corresponds to spatial grain. In freshwaters, this is a wetland,riffle-pool sequence, or defined length of river (Heino, 2011)
Region A region spans multiple locations within an ecologically or environmentally defined area. This could be amajor tributary (sub-basin), drainage basin or ecoregion (Heino, 2011)
Hydrological regime The temporal sequence (frequency, duration and timing) of wetting and drying (hydroperiod; waterregime) and flow events (flow regime) experienced by a freshwater ecosystem (Poff et al., 1997; Brocket al., 2003; Gordon et al., 2004; Boulton et al., 2014). Hydrological regimes encompass hydrologicalvariability across annual, monthly, daily, minutes and millisecond time scales (Biggs, Nikora & Snelder,2005, see also Walker, Sheldon & Puckridge, 1995)
Hydrological disturbance Temporal variation in the hydrological regime that applies a damaging force to an environment occupiedby organisms (Lake, 2000; Cardinale et al., 2005). Disturbances can be predictable or unpredictable(Resh et al., 1988; Poff, 1992)
Environmental flows The protection, allocation and delivery of hydrological regimes to sustain or restore aquatic ecosystems,thereby mitigating undesirable effects of human water use and hydrological alteration
Human exploitation of water and consequent hydrologicalimpacts on rivers, floodplains, and wetlands are consistentlyattributed as causing changes in freshwater biodiversityworldwide (Poff et al., 1997; Bunn & Arthington, 2002;Dewson et al., 2007; Poff & Zimmerman, 2010; Strayer& Dudgeon, 2010). Empirical evidence of biodiversityresponses to altered hydrological regimes has so farconcentrated on relatively fine spatial scales, typically interms of local species richness or average compositionamong sites (Bunn & Arthington, 2002; Dewson et al.,2007; Poff & Zimmerman, 2010). Such an emphasis onlocal biodiversity responses further highlights the limitedconceptual and empirical understanding of effects ofhydrological alteration on freshwater biodiversity across
spatial scales. This gap is problematic because the protection,allocation, and delivery of water for the conservationand restoration of freshwater ecosystems and freshwaterbiodiversity (termed ‘environmental flows’; Table 1) is basedon evidence of the effects of hydrological alteration orhydrological gradients on river and floodplain ecosystems(Olden et al., 2014).
The use of biodiversity as a framework for evaluatingthe performance of hydrological management is pertinentgiven that effects of hydrological change on freshwaterbiodiversity are used as justification for preserving andrestoring hydrological regimes for environmental purposes(e.g. Bunn & Arthington, 2002; Dudgeon et al., 2006; Poff& Zimmerman, 2010). Furthermore, biodiversity change
is central to global assessments of overall biodiversitycondition over time (e.g. McGill et al., 2015), includingin freshwaters (Vorosmarty et al., 2010; Turak et al., 2017).Understanding effects of hydrological regimes on patternsof freshwater biodiversity across spatial scales thereforehas benefits for conceptualising how the managementof hydrological regimes contribute to overall globalbiodiversity.
We contend that the application of spatial scalingis essential for clarifying understanding of the effectsof hydrology on biodiversity in the context of bothfreshwater conservation management and fundamentalecological theory of factors governing biodiversity. Whileenvironmental flows are targeted to preserve or restorefreshwater biodiversity (Acreman et al., 2014; Swirepik et al.,2016), a deficient understanding of biodiversity responses tohydrology across spatial scales means that conceptual theorywill continue to generate confusion and restrict applicationof evidence to informing how environmental flow programscan be applied across multiple spatial scales (Lepori &Hjerdt, 2006). Concepts central to conservation biologyhave not been effectively applied to freshwater conservationmanagement, leading to a sustained gap between freshwaterscience and conservation (Strayer & Dudgeon, 2010).A unified conceptual understanding of the relationships andunderlying ecohydrological mechanisms driving biodiversityacross spatial scales will make a significant contribution toimproving the relevance of freshwater science (sensu Swirepiket al., 2016) to freshwater conservation management. Giventhat freshwaters support the greatest proportion of globalbiodiversity in relation to their small areal extent (Wiens,2015), these environments serve as useful model systems tounderstand fundamental ecological mechanisms that affectbiodiversity.
The target readership for this synthesis is both ecologistswho study the factors responsible for freshwater biodiversityand conservation managers who make decisions aboutthe management of hydrological regimes to protect andenhance freshwater biodiversity. We present a synthesisfor applying concepts of spatial scaling to the mechanisticrelationships between biodiversity and hydrology in surfacewater ecosystems (spanning rivers, floodplains and wetlands).While our synthesis is based on a systematic review of theliterature, our aim is not to attempt a quantitative review(e.g. Poff & Zimmerman, 2010; McMullen & Lytle, 2012) butrather to illustrate how multiple ecohydrological mechanismsmight influence patterns of freshwater biodiversity acrossspatial scales. After briefly defining concepts of biodiversityand spatial scaling, we identify the key components ofhydrological regimes applicable for conceptualising effectson biodiversity. We synthesise the primary evidence ofthe mechanistic roles of hydrology (sensu Sponseller et al.,2013) on patterns of freshwater biodiversity across differentspatial scales to develop a unified conceptualisation. Weconclude with four principles for applying these concepts tohydrological management, and highlight six key themes toaddress gaps in evidence.
II. MULTI-SCALE BIODIVERSITY AS ACONCEPT FOR UNDERSTANDING ECOLOGICALRESPONSES TO HYDROLOGY
(1) Definitions of biodiversity adopted in thissynthesis
Biodiversity is defined as the variety of life forms, includingdiversity within species, between species, and amongecosystems (Gaston, 1996; Gaston & Spicer, 1998; Table 1).Biodiversity is therefore a multi-faceted and multi-scaledconcept that spans variation in the taxonomic, functionaland evolutionary attributes of species (Purvis & Hector,2000; Pavoine & Bonsall, 2011; McGill et al., 2015; Jarzyna& Jetz, 2016). The focus of this synthesis is on biodiversity atthe community level (i.e. multi-species assemblages) because(i) this level of ecological organisation is the most widelyadopted as representative of biodiversity (Magurran, 2004;McGill et al., 2015) and (ii) much of the ecohydrologicalliterature has focussed on this level of organisation (e.g. Lake,2000; Ward & Tockner, 2001; Bunn & Arthington, 2002;Larned et al., 2010; Chester & Robson, 2011). Therefore, wecover assemblages of multiple species that span a range offunctional ecological roles and evolutionary histories.
(2) Spatial scaling of freshwater biodiversity
Despite being intuitively simple, biodiversity is conceptuallycomplex (Hamilton, 2005; Chiarucci, Bacaro & Scheiner,2011) and therefore it is necessary to decompose biodiversityinto a set of measurable and related components (Reyerset al., 2012). Species diversity, as the best-known subset ofbiodiversity (McGill et al., 2015), is expressed as a seriesof components that describe different aspects of the spatialdistribution of species across landscapes. The numbers ofspecies at local and regional spatial extents are defined asalpha and gamma diversity, respectively (Whittaker, 1960;Anderson, Ellingsen & McArdle, 2006; Anderson et al., 2011)whereas spatial variation in community composition acrossa landscape is defined as beta diversity (Anderson et al.,2006). Alpha and gamma diversity share the same unit ofmeasurement (e.g. number of taxa) differing only in terms ofspatial extent, and can be described as ‘inventory’ diversity,whereas beta diversity represents the degree to whichcommunities differ in space (i.e. ‘differentiation diversity’;Jurasinski et al., 2009). Alpha, beta and gamma componentsof diversity can all be applied to each of the three facetsof multi-species diversity (i.e. taxonomic, functional andphylogenetic) (Devictor et al., 2010; Swenson, 2011; Table 1).
Beta diversity is the most complex of these spatialcomponents of biodiversity (Legendre & De Caceres, 2013)and this complexity warrants further description. There aretwo distinct forms of beta diversity: (i) change in compositionalong an environmental gradient (‘directional turnover’) and(ii) non-directional variation in composition among sampleunits within a defined spatial area (Anderson et al., 2011).Variation in composition can be distinguished either in termsof variation among samples within a region, or as variation
Fig. 1. Schematic diagram representing how riverine environments (including floodplains and wetlands) are arranged as a nestedhierarchy of spatial scales and are integrated into analysing and understanding freshwater biodiversity across spatial scales. Thisschematic diagram integrates common terminology of spatial scales adopted in the general ecological literature (aWhittaker et al.,2001), conceptualisations of the hierarchical nature of river-floodplain systems (bFrissell et al., 1986) and applicable measures ofbiodiversity as relevant to each level within the river-floodplain systems (cPavoine et al., 2016).
among regions, reflecting the nested hierarchy of spatialscales and ecological processes structuring communities(see Pavoine, Marcon & Ricotta, 2016). Differences incomposition (directional or non-directional) among samplesor groups of samples are driven by replacement (‘turnover’)and/or loss of taxa, functional traits, or phylogenetic linkages(‘nestedness’) (Baselga, 2010; Carvalho, Cardoso & Gomes,2012; Legendre, 2014). Beta diversity requires that thespecific taxonomic, functional or phylogenetic identitiesof taxa are known (Olden & Rooney, 2006), as separatelocations may have the same number of taxa (alpha diversity)but differ in species identity, for example (see Van Grunsven& Liefting, 2015).
Spatial scaling is fundamental to the measurement of allaspects of biodiversity (Wiens, 1989), and clear definitionsof ‘location’, ‘region’, ‘grain’ and ‘extent’ are necessary forunderstanding biodiversity patterns (sensu Levin, 1992). Whilethere is no consensus on the size applicable to each term(Whittaker et al., 2001), spatial scaling is hierarchically nested(Ward & Tockner, 2001; Heino, Melo & Bini, 2015; Pavoineet al., 2016; Fig. 1). For the purpose of this paper, a location(sensu Wiens, 1989) is a sampling site (e.g. riffle, stream reach,wetland) and sites are located within regions. A region canbe an entire river drainage network (i.e. river basin) ormajor tributary system within a river basin (distinguished onthe basis of geography or hydrology). Finally, spatial extent
spans the entire area included in a study, and therefore maycover multiple regions (Wiens, 1989). These definitions areconsistent with the freshwater biodiversity literature (Heino,2011; Tornwall et al., 2015).
III. THE HYDROLOGICAL BASIS FORFRESHWATER BIODIVERSITY
The hydrological regime of rivers and wetlands is thecombination of the water regime and the flow regime(Table 1). Water regime refers to the temporal pattern ofdrying and wetting of aquatic habitats across the landscape(Boulton et al., 2014, p. 7). The water regime is particularlyrelevant to systems where surface water is not permanent(e.g. floodplains, wetlands, temporary rivers and streams)(e.g. Brock et al., 2003; Larned et al., 2010). Water dynamicscan be determined by methods that measure the temporalsequence of water presence, absence or depth (e.g. Wardet al., 2013; Bhamjee, Lindsay & Cockburn, 2016). Bycontrast, the flow regime represents the temporal sequencein the movement and volume of water passing a pointin space (e.g. water discharging from a tributary into amain channel) and is measured or estimated by streamflowgauges or modelling tools such as rainfall-runoff models.These two elements of the hydrological regime need to be
distinguished because discharge (i.e. flow) cannot occur inthe absence of water, whereas the presence of water canoccur independently of discharge. Each element of thehydrological regime underpins the primary ecohydrologicalmechanisms influencing river–floodplain systems and theirbiodiversity (disturbance, connectivity, habitat; Sponselleret al., 2013). The water regime determines wetting–dryingdynamics and aquatic habitat area (for example), whereasthe flow regime determines variations in channel hydraulicsthat function as disturbances for aquatic organisms (Boultonet al., 2014).
The interaction between temporal and spatial variation(sensu Ward, 1989) in hydrological regimes forms the hydro-logical template for freshwater biodiversity. Temporally,the hydrology of freshwaters describes the sequence oftiming, duration, frequency, magnitude (or depth) and rateof change of events (Poff et al., 1997; Casanova & Brock,2000). Ecological effects of these hydrological events are afundamental theme in freshwater research (Puckridge et al.,1998; Bunn & Arthington, 2002; Biggs et al., 2005; Leira &Cantonati, 2008). Temporal variation in hydrology occursover all possible time scales (e.g. years, months, days, seconds;Biggs et al., 2005), and is driven by the dynamics of rainfall,run-off, evaporation, surface–groundwater interactions,and the freezing and thawing of snow and ice (Euliss et al.,2004; Gordon et al., 2004). The temporal hierarchy concept(Puckridge et al., 1998; Biggs et al., 2005; Fig. 2) hypothesisesthat variation in hydrology occurs over multiple time scalesand different ecohydrological processes and patterns areevident at distinct temporal scales (Biggs et al., 2005). Forexample, rivers in boreal or tropical climates have seasonaland relatively predictable inter-annual hydrological variabil-ity, whereas hydrological variability of arid and subtropicalrivers is most apparent across multiple years (Puckridge et al.,1998; Fig. 3).
Spatial variation in hydrological regimes is also importantin structuring freshwater biodiversity, and occurs both withinand among river networks. Often, headwater streams (firstto second order) drain small catchment areas, and thereforehave rapid fluctuations in discharge (e.g. Baker et al., 2004).By contrast, the presence and movement of water typicallybecomes more permanent as rivers increase in size (e.g. Svec,Kolka & Stringer, 2005), although there are exceptions (e.g.Lake, 2003; Larned et al., 2011). For example, rivers canhave permanent discharge in headwaters before becomingprogressively intermittent (ceasing to flow and often losingsurface water), and then return to permanent discharge inlowlands due to confined upwelling aquifers (e.g. SelwynRiver, New Zealand; Larned et al., 2010). Floodplains havehigh spatial variation in inundation dynamics as a functionof inundation volume, geomorphology, and connection tothe stream network (e.g. Benke et al., 2000; Van Der Natet al., 2002). Spatial variation in hydrology is also evidentamong drainage networks because of differences in climate,geomorphology and land cover (Puckridge et al., 1998;Detenbeck et al., 2005; Poff, Bledsoe & Cuhaciyan, 2006,e.g. Fig. 3).
Fig. 2. Hydrological variability (as discharge variability)expressed across multiple temporal scales: annual (A), monthly(B) and daily (C). The y-axis is scaled by maximum dischargeto emphasise temporal variability independent of differences inmaximum discharge.
IV. BIODIVERSITY RESPONSES TOHYDROLOGICAL REGIMES ACROSS SPATIALSCALES
We systematically reviewed primary evidence documentingresponses of freshwater biodiversity to natural hydrologicalvariation sourced from systematic literature searches usingthe Web of Science (see online Supporting Information:Appendix S1 and Table S1). We deliberately selectedliterature documenting responses to natural hydrologicalvariation because the understanding of natural responsesis necessary to predict effects of anthropogenic changesin hydrological regimes (Fukami & Wardle, 2005; Davies
Fig. 3. Spatial variation in temporal hydrological discharge occurs (A) among and (B) within river basins as a function of differencesin climate, drainage area, geomorphology and land cover. [Sourced from example streamflow gauging stations from the FinnishEnvironmental Institute (Finland), New South Wales Department of Primary Industries (Australia), and the Queensland Departmentof Natural Resources and Mines (Australia)].
et al., 2014). Our synthesis highlights the effects of hydrologyon freshwater biodiversity across spatial scales via the threefundamental mechanistic roles of water (sensu Sponseller et al.,2013; Table 2). First, water acts as a vector for connectivityand movement of energy, material and organisms. Second,water acts as a disturbance for ecosystems and contributesto geomorphic change. Third, water acts as a resource orhabitat for biota.
(1) Effects of hydrological connectivity onfreshwater biodiversity across spatial scales
Hydrological connectivity is a key driver of both local- andlandscape-scale freshwater biodiversity. Increasing hydrolog-ical connectivity predominantly increases taxonomic alphadiversity yet the role of connectivity may depend on how
points in space are connected laterally or longitudinally toriver–floodplain networks. For example, fish species richnessis higher in floodplain pools or wetlands when hydrologicalconnectivity is more prolonged, more frequent, or perma-nent (Lasne et al., 2007; Uchida & Inoue, 2010). However, forother organism groups, effects of connectivity are less consis-tent. Taxonomic alpha diversity of macroinvertebrates anddiatoms may peak at intermediate levels of hydrological con-nectivity (Van Den Brink et al., 1996; Gallardo et al., 2014).Effects of hydrological connectivity on macrophyte alphadiversity are variable, with higher numbers of taxa occur-ring in hydrologically connected (compared to fragmentedsites; e.g. Akasaka & Takamura, 2012) or in fragmented ormore frequently isolated sites versus permanently connectedsites (e.g. Keruzore et al., 2013). Hydrological connectiv-ity positively influenced alpha diversity of aquatic bacteria
(e.g. Fazi et al., 2013), periphyton (e.g. Algarte et al., 2009)and macroinvertebrates (Starr et al., 2014) and this effect isevident both in terms of connectivity between floodplainwetlands and their associated stream network, and also insite-to-site connectivity within stream channels.
Effects of hydrological connectivity on local-scalefunctional diversity are much more variable and less wellunderstood than effects of taxonomic diversity. Hydrologicalconnectivity was positively associated with functional alphadiversity of waterbirds in wetlands of lowland floodplainrivers in Brazil (Almeida et al., 2017). By contrast, functionalalpha diversity of floodplain macroinvertebrate assemblagespeaked in periods of relatively intermediate hydrologicalconnectivity and was lower for highly fragmented and highlyconnected sites (Paillex et al., 2013; Gallardo et al., 2014).These inconsistencies likely reflect the fact that differentorganism groups are used to test connectivity–diversityrelationships, but may also reflect differences in thespatial (longitudinal versus lateral; Amoros & Bornette,2002) and temporal (duration and frequency) aspects ofhydrological connectivity. Inconsistencies may also resultfrom comparisons between groups of sites that arehydrologically connected at the time of field surveys butare not permanently connected.
Empirical evidence shows that hydrological connectivityis an important determinant of compositional variability ofassemblages across landscapes (beta diversity) for multipleorganism groups, as predicted by conceptual models(Thomaz et al., 2007; Larned et al., 2010). Beta diversityof bacteria, fish, macroinvertebrates and macrophytes isgenerally lowest in river–floodplain or wetland complexesduring periods of high hydrological connectivity mediatedby flood inundation, and increases during water recessionas sites within rivers or river–floodplain networks becomeprogressively fragmented (e.g. Fernandes et al., 2009; Gomeset al., 2012; Fazi et al., 2013; Starr et al., 2014). However,when multiple organism groups are analysed simultaneouslyfrom one study system, the effect of temporal variationin hydrological connectivity on compositional variabilityvaries with dispersal ability (Padial et al., 2014). Differencesin taxonomic composition along hydrological connectivitygradients (e.g. Algarte et al., 2009) provide further evidencefor the role of connectivity as a mechanism linking hydrologyand freshwater beta diversity.
(2) Effects of hydrological disturbance onfreshwater biodiversity across spatial scales
Environmental disturbances affect biological communities(Resh et al., 1988; Poff, 1992; Lake, 2000). At local scales,hydrological disturbances impact freshwater organisms viathe process of physical scouring (by flooding) and desiccationof organisms (by drying). The effects of hydrologicaldisturbance on alpha diversity vary for flooding anddrying disturbances. Unprecedented drying events reducedmacroinvertebrate alpha diversity in arid-climate streamsin the USA (Bogan & Lytle, 2011), and richness ofmacroinvertebrate assemblages is negatively associated
with increasing hydrological ‘harshness’ (including channeldrying) (Fritz & Dodds, 2005). Effects of flooding disturbancesare more complex, with the response of macroinvertebrateand macrophyte alpha diversity to flooding frequencyor intensity ranging from hump-shaped (e.g. Townsendet al., 1997; Riis et al., 2008), supporting the intermediatedisturbance hypothesis (Connell, 1978), to linear (eitherpositive or negative; e.g. Death & Winterbourn, 1995;Bornette, Amoros & Lamouroux, 1998). The effect offlood disturbance frequency on alpha diversity of benthicalgae appears to depend on the degree of substratumarmouring (e.g. Biggs & Smith, 2002). This findingsuggests that both physical characteristics of study sites andbiological traits of study organisms influence the relationshipbetween hydrological disturbances and local biodiversity.Additionally, discrepancies among studies may be due todifferences in the severity of hydrological disturbances andthe fact that a broad spectrum of disturbances is rarelyincluded in individual studies (Riis et al., 2008). However,patterns of recovery of local species richness with increasingtime since flood disturbance are broadly consistent amongstudies (e.g. Greenwood & Booker, 2015).
Hydrological disturbances can also affect functionalalpha diversity of freshwater organisms. Functional diversityof benthic biofilm assemblages was significantly reducedby stream-drying disturbances (Timoner et al., 2014) yetmacrophyte functional richness did not differ in floodplainlakes that varied in drying disturbance frequency (Arthaudet al., 2012). The predictability and variability of discharge(as measures of disturbance) are also strongly associatedwith the prevalence of functional traits of riverine fish insites across the USA (Mims & Olden, 2012; McManamay,Bevelhimer & Frimpong, 2015). Yet it is unknown whetherthis variation in trait prevalence translates into variation inlocal functional-trait richness in aquatic systems.
At landscape scales, spatial variation in hydrologicaldisturbance regimes affects both taxonomic and functionalbeta diversity. In floodplain lakes, waterbird taxonomiccomposition differed significantly between hydrologicallystable lakes and lakes that were more disturbed by water-levelfluctuations (Kingsford et al., 2004). Spatial variation infunctional composition of fish assemblages can reflect spatialgradients of discharge variability (Poff & Allan, 1995).Hydrological disturbances also alter beta diversity betweensites with similar hydrology. For example, spatial variation inmacroinvertebrate composition among experimental pondswith drying disturbances was significantly lower than spatialvariation among permanently wetted ponds (Chase, 2007).
Hydrological disturbances also strongly affect regionalgamma diversity. Fish have been the primary organismgroup for researching differences in basin-scale biodiversityassociated with hydrology (see Table S1, SupportingInformation). Iwasaki et al. (2012), McGarvey (2014); Jardineet al. (2015) and McGarvey & Terra (2016) each comparedregional gamma diversity of fish across different parts of theglobe [e.g. Northern Hemisphere (Iwasaki et al., 2012) andtropical regions (Jardine et al., 2015)] and related the total
number of species to temporal discharge variability. Across allof these studies, there was a consistent and significant negativerelationship between increasing hydrological variability (e.g.inter-annual variation in discharge) and fish gamma diversity,suggesting that hydrological disturbances constrain regionaldiversity (Iwasaki et al., 2012; McGarvey, 2014; Jardine et al.,2015; McGarvey & Terra, 2016). However, it is unknownwhether this relationship applies to other organism groups.
(3) Effects of hydrological habitat gradients onfreshwater biodiversity across spatial scales
Hydrology strongly affects freshwater biodiversity aswater presence and discharge determine habitat spatialextent, temporal persistence and hydraulics. Two majorhydrological gradients are evident in the primary literatureas being determinants of freshwater biodiversity. First, thereis a strong effect of the duration of surface water (termed‘hydroperiod’) on local biodiversity. For example, taxonomicalpha diversity of fish and macroinvertebrates is positivelyassociated with hydroperiod duration (e.g. Chakona et al.,2008; Beesley & Prince, 2010; Datry, 2012; Datry, Corti& Philippe, 2012; Bogan et al., 2013; Datry et al., 2014b).In addition to taxonomic alpha diversity, hydroperiod alsoaffects functional alpha diversity through the prevalenceof traits favoured by drying (Bogan et al., 2013). Second,a decline in local species richness is linked with lossof specific in-stream habitats that are necessary for thepersistence of specialised taxa. For example, inundation ofriffles strongly depends on stream discharge, and thereforethe loss of riffles is linked with removal of taxa thatrequire flowing water for habitat or feeding [as foundin studies of the effects of reductions in water dischargeor differences between perennially and non-perenniallyflowing streams (e.g. Feminella, 1996; Boulton, 2003; Rose,Metzeling & Catzikiris, 2008; Santos & Stevenson, 2011;Warfe et al., 2014)]. However, effects of habitat permanenceon local taxonomic richness are strongly determined byseasonality. Clarke et al. (2010), for example, found thatdifferences in local macroinvertebrate richness amongpermanently, intermittently and ephemerally flowing sitesoccurred during periods where hydrological differences weregreatest among sites. Rapid recovery of local assemblagestook place as discharge returned, particularly in ephemeraland intermittent streams (Clarke et al., 2010).
Beyond in-stream sites, hydroperiod strongly affects localfloodplain, riparian, and wetland biodiversity, yet thereis variation in the shape of the response to hydroperiodgradients. Increasing taxonomic alpha diversity of floodplainor riparian vegetation assemblages is positively linkedwith frequency or duration of flooding and streamflowpermanence (e.g. Capon, 2005; Stromberg et al., 2005).By contrast, taxonomic alpha diversity of either wetlandmacrophytes or riparian vegetation was greatest atintermediate (Katz et al., 2012; Nielsen et al., 2013) orlow (Pettit et al., 2001) inundation frequency or duration.Functional alpha diversity of riparian vegetation waspositively affected by inundation variability (Lawson et al.,
2015). These findings suggest that aspects of floodplaininundation (frequency, duration, and therefore temporalvariability) affect taxonomic and functional alpha diversity offloodplain plant communities although evidence remainslimited to determine if both taxonomic and functionalfacets of biodiversity respond in similar ways to individualhydrological gradients.
Water permanence in wetlands or floodplain lakes posi-tively affects alpha diversity of diatoms, fish and macroin-vertebrates (Table 2). Across tropical, temperate and aridenvironments, fish species richness in floodplain wetlandsincreases with increasing persistence and depth of sites (e.g.Puckridge, Costelloe & Reid, 2010; Penha et al., 2017). Asimilar relationship is evident for wetland diatoms andmacroinvertebrates with local species richness increasingwith increasing duration of wetland inundation (e.g. Silveret al., 2012; Chessman & Hardwick, 2014). Importantly, oneof the few studies that test relationships between hydrologyand phylogenetic diversity found a positive effect of water per-manence on local phylogenetic diversity (Silver et al., 2012).
Stream discharge magnitude and duration affectstaxonomic alpha diversity but responses vary amongorganism groups. Reduced discharge during hydrologicaldroughts lower alpha diversity of fish and macroinvertebratesin rivers (e.g. Clarke et al., 2010; McCargo & Peterson, 2010),and spatial comparisons have found a positive effect ofstream-discharge permanence on local taxonomic richness(e.g. Leigh & Datry, 2017). Taxonomic alpha diversitycan be more strongly associated with minimum than withmean flow magnitude (Konrad et al., 2008) or can beassociated with stream cross-sectional area (McHugh et al.,2015). Relationships between discharge permanence andthe number of macroinvertebrate families vary in terms ofphylogeny. For example, the number of macroinvertebratefamilies within each of the orders Ephemeroptera, Plecopteraand Trichoptera increased with discharge permanenceand magnitude whereas the opposite response was foundfor the number of families of Odonata, Coleoptera,Heteroptera and Diptera (Belmar et al., 2013). This mayreflect broad differences in preferences for fast-flowing waterby Ephemeroptera, Plecoptera and Trichoptera (EPT) taxaand slow-flowing (or no-flow) water by Odonata, Coleoptera,Heteroptera and Diptera (OCHD) taxa. Similar family-basedtaxonomic diversity relationships occur for fish, suggestingthat hydrology–biodiversity relationships are influenced byevolutionary history. For example, alpha diversity of speciesin the families Centrachidae and Cyprinidae was positivelyassociated with temporal discharge variability, whereasdischarge magnitude was positively linked with richness ofspecies in the families Catostomidae and Percidae in theUSA (Niu et al., 2012).
Spatial variation in the hydrology of river and floodplainenvironments is an important determinant of biodiversityat landscape scales, and many of the hydrological gradientsinfluencing aquatic habitat or aquatic resource dynamicsidentified above strongly influence patterns of beta diversitybut in different ways from local-scale patterns. Spatial
variation in the duration or frequency of surface-waterpresence strongly affects spatial variation in taxonomicand functional composition of fish, macroinvertebrate,riparian plant and waterbird assemblages (Table 2). Forexample, spatial differences in taxonomic compositionwithin river–floodplain systems are consistently reportedin association with differences in surface-water permanencein both stream networks [e.g. USA, New Zealand, Europe,Australia (Stromberg et al., 2005; Datry et al., 2007, 2014a;Beesley & Prince, 2010; Bogan et al., 2013; Tornes & Ruhí,2013)] and floodplain wetland or riparian communities (e.g.Kingsford et al., 2004; Davidson et al., 2012; Nielsen et al.,2013; Chessman & Hardwick, 2014). Where reported in theliterature, nestedness is the dominant driver of compositionalchange along hydroperiod gradients (e.g. Datry et al.,2014a). Compositional turnover (i.e. replacement) occursin some systems or organism groups whereby taxa lost frompermanently inundated sites are replaced by taxa adapted todesiccation or recolonisation in temporarily inundated sites(e.g. Bogan et al., 2013).
Spatial variation in streamflow hydraulics is also animportant determinant of taxonomic beta diversity, bothwithin and among landscapes. Studies of biodiversityresponses to spatial heterogeneity of discharge havefocused heavily on macroinvertebrates, with differencesin the assemblage composition among reaches or wholerivers associated with differences in discharge patterns(e.g. Feminella, 1996; Leigh & Sheldon, 2009; Clarkeet al., 2010; Warfe et al., 2014; Leigh & Datry, 2017).Significant changes in composition along discharge gradientsalso occur for other organism groups, such as aquaticbacteria (Besemer et al., 2009). Within-group compositionalvariability is often different for different hydrology (i.e.the magnitude of variation in composition among samplescan be greater for particular hydrological conditions). Forexample, spatial variation in macroinvertebrate compositionwithin ephemerally flowing headwaters was greater thanthat of perennially flowing streams, especially during dryseasons (Clarke et al., 2010), whereas the macroinvertebratecommunities were more variable in perennially flowing thanin intermittently flowing streams (Warfe et al., 2014).
Analyses based on data sets spanning multiple continentsconsistently show positive effects of annual discharge atthe scale of entire river basins on taxonomic gammadiversity (Oberdorff et al., 1995; Xenopoulos et al., 2005;Xenopoulos & Lodge, 2006; Iwasaki et al., 2012; McGarvey,2014). In this context, discharge magnitude is viewed asanalogous to geographical area in terrestrial species–arearelationships, because an increasing volume of water createsgreater space. Such relationships have been queried becauseregional species richness is not necessarily in equilibriumwith contemporary hydrology (Olden et al., 2010). Similar toresponses of local biodiversity to discharge, mean-annual-lowflow discharge was a stronger predictor of drainagebasin-scale fish species richness in the Americas (McGarvey& Terra, 2016), suggesting that minimum habitat volumesconstrain gamma diversity.
V. A CONCEPTUAL MODEL OF THEHYDROLOGICAL DRIVERS OF MULTI-SCALEDFRESHWATER BIODIVERSITY
Evidence from empirical studies indicates that differentecohydrological mechanisms vary in how they influencebiodiversity at different spatial scales (Table 2). In anattempt to unify these mechanisms, we present a conceptualmodel to summarise how different facets of biodiversityacross different spatial scales vary in response to hydrologyof river–floodplain systems (Fig. 4). In spatial terms, themodel is structured around the mechanisms that influencebiodiversity at regional scales, among landscapes, withinlandscapes, and at local scales (sensu Pavoine et al., 2016).In the context of the hierarchical nature of river networks,the model is based on identifying mechanisms structuringbiodiversity among rivers basins (as regions), among majortributaries within basins (as landscapes), among reacheswithin major tributaries, and at the reach scale.
At the scale of river basins, disturbance and habitat areprimary ecohydrological drivers of freshwater biodiversity(Fig. 4). Regional biodiversity is positively influenced byaquatic habitat size (indicated by discharge volume), andconstrained by disturbance history (e.g. temporal dischargevariability). Disturbance constraints likely explain whydrainage basins with high inter-annual variation in dischargesupport fewer fish species than other comparably sized riverbasins with more predictable hydrology (e.g. Puckridge et al.,1998; Jardine et al., 2015). In contrast to biodiversity atsmaller spatial scales (i.e. within regions), current connectivityhas little effect on regional biodiversity (although historicalhydrological fragmentation may be important for gammadiversity because of vicariance leading to speciation events)(e.g. Griffiths, 2010). A gap in evidence of the effectsof hydrological regimes on phylogenetic and functionaldiversity restricts the ability to make explicit predictionsof these facets of biodiversity at regional scales. However,evidence of the roles of habitat persistence and disturbance atfiner spatial scales suggests that phylogenetic and functionaldiversity are positively influenced by habitat size andnegatively influenced by hydrological disturbance.
Spatial variation in taxonomic and functional compositionamong landscapes is influenced by habitat and disturbance(Fig. 4). In contrast to regional-scale biodiversity, theemphasis at landscape scales is on how assemblages varytaxonomically, functionally and phylogenetically in responseto ecohydrological mechanisms. Spatial variation in habitatrelated to hydrological variables such as hydroperiod ordischarge duration, and in hydrological disturbance regimesis linked positively with spatial variation in freshwaterbiodiversity among landscapes (e.g. Leigh & Sheldon, 2009;Warfe et al., 2014).
In contrast to among-landscape variation, biodiversitywithin landscapes depends on each of the majorecohydrological variables and connectivity is importantat this spatial scale of biodiversity (Fig. 4). Hydrologicalconnectivity negatively affects taxonomic and functional
Fig. 4. A conceptual model summarising patterns of biodiversity across multiple spatial scales along distinct ecohydrologicalgradients in surface water and floodplain environments. The direction of each arrow along the gradient of increasing–decreasingbiodiversity represents the shape of the effect of each ecohydrological mechanism, for each spatial scale of biodiversity. For example,increasing temporal discharge variability leads to decreasing regional biodiversity. Other variables unrelated (or only indirectlyrelated) to hydrology (e.g. latitude, geomorphology, surrounding catchment characteristics) are not included but recognised asrelevant to structuring freshwater biodiversity across spatial scales. The positive and negative effects of hydrological disturbanceregime and local-scale biodiversity reflect contradictory and hump-shaped responses reported in the literature (see text for furtherdetails).
biodiversity because of greater opportunities for dispersal(Akasaka & Takamura, 2012). Spatial heterogeneity inphysical habitat persistence and hydraulic habitat conditions,both mediated by the hydrological regime, positivelyaffect landscape-scale biodiversity (e.g. Lamouroux, Poff &Angermeier, 2002; Horrigan & Baird, 2008; Sim et al., 2013).Hydrological disturbance has multiple effects on landscapebiodiversity; disturbances that affect entire landscapes (e.g.droughts) lead to reduced spatial variation in compositionby removing organisms with patchy distributions orspecialised ecological niches that are unable to resist thedisturbances (e.g. Chase, 2007). However, where the timingand magnitude of hydrological disturbances are spatiallyvariable within the landscape, taxonomic and functionalbeta diversity increase (e.g. Bogan et al., 2013). This
matches the heterogeneous disturbance hypothesis originallyproposed for terrestrial landscapes (Warren et al., 2007) andhas substantial application to hydrological disturbances infreshwaters.
At local spatial scales, freshwater biodiversity is influencedby a broader combination of ecohydrological mechanisms(Fig. 4). Here, hydrological connectivity often positivelyinfluences local functional and taxonomic richness, at leastup to a point (e.g. Lasne et al., 2007; Paillex et al., 2013).Disturbance impacts depend primarily on the breadth of thedisturbance gradient; increasing flood disturbance impactson local taxonomic diversity by progressively removingtaxa via scour processes (e.g. Biggs & Smith, 2002), yethydrological disturbance frequency or intensity can producea unimodal response of alpha diversity (e.g. Riis et al., 2008),
Table 3. Principles for developing a multi-scaled understanding of biodiversity responses to hydrological regimes
Principle Premise
1. Understanding biodiversity responses to hydrologicalregimes across spatial scales is essential for quantifying thetrue impacts of hydrological regime change on freshwaterbiodiversity
Empirical research and conceptual understanding of the effects ofanthropogenic changes to hydrological regimes hasinadequately considered how responses of biodiversity varyacross different spatial scales
2. Effects of hydrological regime change on freshwaterbiodiversity are best addressed when the specific spatialscale(s) of impact and underlying ecohydrologicalmechanisms are identified
Application and delivery of environmental flow programs will bestachieve desired biodiversity targets when the spatial scales ofbiodiversity responses to hydrological regimes are understoodand linked to specific ecohydrological mechanisms
3. Risks of environmental flows as a driver of furtherbiodiversity decline can be addressed and managed whenlinks between hydrological regimes and freshwaterbiodiversity are tied to spatial scaling
Poor consideration of how hydrological regimes influencefreshwater biodiversity across spatial scales means that there is arisk that environmental flow programs may contribute tobiodiversity loss at specific spatial scales
4. Biodiversity responses to hydrological regimes across spatialscales depend on the biological and ecological characteristicsof organisms used for assessment
Effects of hydrological regimes on patterns of biodiversity acrossspatial scales are variable among different organism groups
supporting the intermediate disturbance hypothesis. Aquatichabitat persistence, volume, and within-habitat hydraulicvariability each positively drive functional and taxonomicrichness (e.g. Clarke et al., 2010; Timoner et al., 2014;McHugh et al., 2015).
VI. PRINCIPLES AND APPLICATIONS OF AMULTI-SCALED CONCEPTUALUNDERSTANDING OF FRESHWATERBIODIVERSITY RESPONSES TOHYDROLOGICAL REGIMES
An overarching goal of freshwater conservation policiesglobally is to sustain and restore the biodiversity of freshwaterecosystems [e.g. National Principles for the Provision ofWater for Ecosystems (ARMCANZ & ANZECC, 1996;Arthington & Pusey, 2003); European Water FrameworkDirective (Acreman & Ferguson, 2010)]. However, the lack ofgeneral theory of the multi-scalar and multi-faceted responsesof biodiversity to hydrological alterations is likely a barrierto the success of water policies and environmental flowsin meeting biodiversity targets. We detail four principles toenhance a conceptual understanding of how hydrologicalregimes affect freshwater biodiversity across spatial scales(Table 3). In so doing, we highlight how the restoration ofhydrology via environmental flows can benefit freshwaterbiodiversity from an explicit consideration of spatialscaling.
(1) Principle 1: understanding biodiversityresponses to hydrological regimes across spatialscales is essential for quantifying the true impactsof hydrological change on freshwater biodiversity
Empirical evidence of the impacts of hydrological alterationon freshwater biodiversity is used widely to justifythe provision of hydrological regimes to sustain or
restore freshwater biodiversity (e.g. Bunn & Arthington,2002; Poff & Zimmerman, 2010). However, the trueextent of the consequences of anthropogenic hydrologicalchange for freshwater biodiversity are almost certainlyunderestimated, because freshwater biodiversity researchhas inadequately dealt with issues of spatial scaling whenquantifying impacts of hydrological change on specific spatialcomponents of freshwater biodiversity. In addition, theeffects of hydrological change on phylogenetic diversity ofcommunities across spatial scales are simply not representedin the hydrological alteration literature (e.g. Poff &Zimmerman, 2010), and evidence of functional biodiversityresponses to hydrological change remains extremely limited.
Inventories of taxa at local scales (i.e. alpha diversity)are used extensively as biodiversity indicators for freshwaterbiomonitoring programmes (e.g. Davies et al., 2010; Carlisle,Wolock & Meador, 2011), studying the effects of hydrologicalalteration (e.g. Kingsford et al., 2004; Nielsen et al., 2013),and evaluating the performance of restoration of freshwaterecosystems (e.g. Palmer, Menninger & Bernhardt, 2010;Yang et al., 2016). However, as the simplest attribute,alpha diversity reflects only a single aspect of biodiversity(Angermeier, 2010; McGill et al., 2015). Use of local-scalebiodiversity responses to hydrological regimes may beinsensitive to change when compared to other spatialcomponents of biodiversity. For example, taxonomic alphadiversity of macroinvertebrates did not differ betweenregulated (sustained low-flow) and unregulated reaches(variable intra-annual discharge) in California (USA), yetwithin-reach beta diversity was significantly lower in theregulated reach (Marchetti et al., 2011), and higher fish betadiversity was evident in unregulated versus regulated reachesin the eastern USA (Freedman et al., 2014). Beyond thecontext of hydrological change, measures of biodiversitythat assess spatial variation in assemblage compositionare more responsive to anthropogenic disturbancesand conservation management actions (e.g. Passy &Blanchet, 2007).
Further compounding the issue is that few studies examin-ing biodiversity responses to hydrological change simultane-ously assess effects across the full range of spatial scales thatoccur in the spatial hierarchy of freshwater systems (i.e. areimpacts of hydrological alteration more evident at specificspatial components of biodiversity?). Assessing the responsesof biodiversity to hydrological alteration at single spatialscales constrains understanding to focus only on that spe-cific spatial scale (sensu Levin, 1992), while ignoring potentialand more-severe responses at other spatial scales. A criticalpoint here is that some studies quantify the number of taxapresent at multiple spatial extents within rivers (e.g. samples,sites, reaches) in association with differences in hydrology(e.g. Robson, Hogan & Forrester, 2005). Such studies makecomparisons of taxon richness across differing areas (sensuWiens, 1989; Jurasinski et al., 2009), yet do not address otherimportant aspects of biodiversity (e.g. spatial variation incomposition) across the spatial hierarchy of freshwater net-works. By contrast, simultaneous assessment of biodiversityacross the multiple hierarchical levels of freshwater systems(sensu Pavoine et al., 2016) is hypothesised to give a muchstronger and more practical understanding of how hydrolog-ical regimes influence biodiversity across spatial scales.
(2) Principle 2: effects of hydrological change onfreshwater biodiversity are best addressed whenthe specific spatial scale(s) of impact and underlyingecohydrological mechanisms are identified
The failure to consider explicitly how different facetsof biodiversity respond to environmental gradients acrossspatial scales has been identified as a fundamentalimpediment to addressing anthropogenic impacts to protectbiodiversity (McGill et al., 2015). Following from Principle 1,it is essential that efforts to preserve or restore hydrologicalregimes are delivered at the spatial scale at which impacts ofanthropogenic hydrological regime change are most evident.Despite hydrological regime alteration being typicallyapparent at spatial extents covering >101 km of rivernetworks, most studies examining the responses of freshwaterbiodiversity are based on data from study sites spanning<10−1 km (Table 2; Poff & Zimmerman, 2010), concordantwith the spatial scale of freshwater biodiversity research moregenerally (Tornwall et al., 2015). If the impacts of hydrologicalchange on freshwater biodiversity are greater at spatial scaleslarger than individual study sites, but these impacts are notquantified, then there is an increased risk that restorationof elements of natural hydrological regimes will not meettargeted levels of biodiversity response. This situation reflectsthe need to match the spatial scales of research to (i)questions of ecological interest, and (ii) test hypothesesat scales that are relevant to conservation actions (sensuFausch et al., 2002). If hydrological change differentially altersbiodiversity across spatial scales (e.g. Pegg & Taylor, 2007)then we hypothesise that maintaining or restoring aspects ofhydrological regimes across the spatial scales where impactsare most evident is likely to produce the most apparentrecovery of freshwater biodiversity. For example, a minor
effect of hydrological alteration on local biodiversity but moresubstantial impact on landscape-scale biodiversity wouldsuggest a need to coordinate the delivery of environmentalflows within and between river basins (potentially achievedby spatially desynchronising the delivery of environmentalflow programs among river basins.
The success of implementing environmental flows toachieve the goal of protecting and enhancing freshwaterbiodiversity across spatial scales is likely to be improved if theunderlying causal mechanisms linking hydrological changeand biodiversity responses across spatial scales are known. If aspecific mechanism is identified as linking hydrological alter-ation to biodiversity responses at particular spatial scales, thenthe restoration of hydrological regimes by environmentalflows can be tailored around the frequency, timing, durationand magnitude of hydrological events (sensu Poff et al.,1997) that confer the environmental conditions to restorebiodiversity at the spatial scale of interest. Clearly, ecohy-drological mechanisms are unlikely to produce consistentresponses for different organism groups (due to differencesin biology and ecology; see Principle 4). However, linkinghydrology to biodiversity responses across spatial scales viaspecific ecohydrological mechanisms will almost certainlybetter equip water-management policies with the evidenceto preserve freshwater biodiversity at scales of interest.
(3) Principle 3: risks of environmental flows as adriver of further biodiversity decline can beaddressed and managed when links betweenhydrological regimes and freshwater biodiversityare tied to spatial scaling
Environmental flows are widely advocated and used as a toolfor freshwater biodiversity conservation (Poff & Matthews,2013; Acreman et al., 2014). However, a poor considerationof how hydrology influences freshwater biodiversity acrossspatial scales creates the paradoxical situation whereenvironmental flows may inadvertently contribute to furtherlosses of biodiversity. These risks are critical to recognisebecause environmental flows often come at a cost to otherwater users (e.g. economic consequences of reduced wateravailability for human uses) or because of public investmentin water intended for biodiversity benefits.
One potential risk of an inadequate understanding of therelationships between hydrological regimes and freshwaterbiodiversity across spatial scales is loss of spatial variation inassemblage composition. Termed ‘biotic homogenisation’,declines in spatial variation in biodiversity is one aspect ofglobal biodiversity decline (McKinney & Lockwood, 1999;McGill et al., 2015) that can be identified only when spatialvariation in community composition (taxonomic, functional,or phylogenetic) is tied explicitly to spatial scale (Rooneyet al., 2007). Homogenisation of freshwater communitiesis often examined in the context of the spread andestablishment of non-native fauna (e.g. Villeger et al., 2011),but biotic homogenisation can also occur independently ofnon-native species (e.g. Lougheed et al., 2008; McCune &Vellend, 2013; Trentanovi et al., 2013; Li & Waller, 2015;
Perkin et al., 2015). However, because spatial variation infunctional and taxonomic composition within and amongriver networks is tied to spatial variation in hydrology(Table 2), environmental flow programs that fail to accountfor spatial variability across larger spatial extents may leadto biodiversity loss at landscape scales but preservation ofbiodiversity at local scales. This possibly creates a paradoxfor conservation management whereby actions designed topreserve or enhance biodiversity may inadvertently con-tribute to biodiversity loss due to inadequate considerationof how biodiversity responses vary across spatial scales.
Our emphasis on beta diversity and risks to biodiversityvia environmental flows here is important because thiscomponent of biodiversity is often overlooked when planningand communicating outcomes of hydrological regimechange. For example, changes to future hydrology andconsequences for freshwater biodiversity focus heavily onaspects of ‘inventory’ diversity (sensu Jurasinski et al., 2009; e.g.Palmer et al., 2008). However, water resource developmenthas reduced spatial variation in hydrological regimes atmultiple spatial scales (within rivers, e.g. Thoms & Parsons,2003; among rivers, e.g. Poff et al., 2007). Alternatively,there is also evidence that dams have caused hydrologicalregimes to become more spatially variable (McManamay,Orth & Dolloff, 2012). Evidence of the effects of hydrologicalchange on spatial variation in biodiversity remains a keyknowledge gap (Poff et al., 2007; Rahel, 2010), yet suchevidence is essential to ensuring that environmental flowsdo not contribute further to biodiversity loss via biotichomogenisation.
(4) Principle 4: biodiversity responses to hydrologyacross spatial scales depend on the biological andecological characteristics of organisms used forassessment
Inconsistencies in the relationships between hydrologyand freshwater biodiversity across spatial scales amongdifferent organism groups can create further uncertainty forfreshwater conservation managers for managing hydrology.The ecological and biological characteristics of differentorganism groups (e.g. riparian plants, riparian fauna, fishand waterbirds) have a major role in determining theeffect of hydrological regimes on freshwater biodiversity.Importantly, aspects of hydrology can simultaneously affectthe biodiversity of different organism groups in contrastingways via different ecohydrological mechanisms. For example,alpha diversity of riparian macroinvertebrates increases withtime since inundation (Datry et al., 2012), indicating thatinundation of riparian zones by flooding acts as a disturbancefor riparian invertebrates, whereas alpha diversity of riparianvegetation communities increases with water permanence,highlighting the importance of water as a resource for plants(Stromberg et al., 2005).
Differences in the responses of biodiversity to hydrologyacross spatial scales among organism groups underscoresthe need to understand the effects of hydrology on specificorganism groups. Few studies compare responses of different
organism groups to environmental gradients in aquaticecosystems (Johnson et al., 2014), and this deficiency isevident in our review of the literature (Table S1, SupportingInformation). In a study comparing ecological characteristicsof intermittently and permanently flowing rivers in Tasma-nia, Australia, Warfe et al. (2014) found that while differencesin assemblage composition between flow regimes were clearfor riparian vegetation, biofilms, and macroinvertebrates(i.e. beta diversity), responses of alpha diversity to differencesin flow regime were inconsistent among organism groups.This finding highlights that biological and ecologicalattributes (e.g. life-history, trophic ecology and habitatpreference) of the specific organism group need to beevaluated when conceptualising the role of hydrology infreshwater biodiversity and making recommendations forenvironmental flows to protect or enhance it.
VII. FUTURE RESEARCH OPPORTUNITIES FORADVANCING A CONCEPTUAL UNDERSTANDINGOF HYDROLOGY – BIODIVERSITY LINKAGES
Synthesising evidence of the effects of hydrological regimeson freshwater biodiversity across its multiple facets and spatialcomponents highlights that important gaps in knowledge stillremain within the topic of ecohydrology. Here, we emphasisesix key topics for refocussing research to strengthen our abilityexplicitly to understand and predict biodiversity responses tohydrological regimes (Table 4).
(1) Simultaneous multi-scaled assessment ofbiodiversity responses to hydrology
Most research of the effects of hydrology on biodiversityhas examined the responses of a single spatial componentof biodiversity (Bunn & Arthington, 2002; Poff & Zimmer-man, 2010; Table S1, Supporting Information). Focussingon single aspects of biodiversity (e.g. inventory, differen-tiation; Jurasinski et al., 2009), leads to conclusions beingapplicable only to that specific spatial component and facetof biodiversity and therefore neglecting the influence ofhydrology on biodiversity at other scales. For example,numerous studies show that increasing the duration of surfacewater persistence increases local taxonomic and functionalrichness (Section IV). However, increasing surface water per-sistence often occurs in conjunction with greater hydrologicalconnectivity, which decreases spatial variation in composi-tion among sites. While comparisons among geographicallydisparate studies help disentangle the effects of differentecohydrological mechanisms on patterns of freshwater biodi-versity, few studies assess effects of hydrology on biodiversityresponses across different spatial components of biodiversitysimultaneously across the spatial extent of analysis.
The benefit of adopting a multi-scaled approach toquantifying biodiversity responses to hydrological regimes isthat the mechanism(s) influencing each spatial componentof biodiversity can be identified (e.g. Edge et al., 2017)
Test how separate spatial components ofbiodiversity vary in response to hydrologicalgradients within specified spatial extents
Ecohydrological mechanisms responsiblefor variation in each spatial componentof biodiversity are identified
Concordance of biodiversity responsesto hydrological mechanisms amongmultiple organism groups
Sample multiple organism groups across thespatial hierarchy of river–floodplainnetworks and compare how biodiversityresponses to hydrological regimes varyamong organism groups
Informative to developing monitoringprograms to evaluate outcomes ofenvironmental flow programs onfreshwater biodiversity
Multi-faceted biodiversity responses tohydrological regimes across spatialscales
Analyse patterns of taxonomic, functional, andphylogenetic biodiversity across spatialscales and test how variation in spatialcomponents of biodiversity is associatedwith ecohydrological gradients
Addresses major gaps in understanding theeffects of hydrological regimes (orhydrological regime change) onfunctional and phylogenetic facets ofbiodiversity across spatial scales
Combined use of natural andanthropogenic hydrological gradientsto improve confidence of biodiversityresponses to hydrological regimes
Compare how patterns of biodiversity arelinked with ecohydrological mechanismsalong separate natural and anthropogenichydrological gradients
Inferences of the effects of hydrologicalregimes on biodiversity are strengthenedwhen natural and anthropogenicgradients are used in combination
Temporal change in spatial biodiversitypatterns
Test how different spatial components ofbiodiversity vary over time in response toecohydrological events (e.g. floodingdisturbance, inundation that enhancesconnectivity or prolongs habitat persistence)
Spatial components of biodiversity thatrespond more rapidly and consistently tohydrological events can be targetedduring the design and evaluation ofenvironmental flow programs
Replicate designed studies of biodiversitypatterns across regions that have distinctclimate and hydrological characteristics (e.g.differences in hydrological regimepredictability)
Increases ability to develop broadgeneralisations of biodiversity responsesto hydrological regimes and identify howthe effects of hydrological regimes aredependent on other environmentalvariables
and therefore addressed more precisely by environmentalflows. Multi-scaled assessment of biodiversity responses tohydrology could be analysed in ways that reflect the nestedhierarchy of riverine environments. Pavoine et al. (2016) pro-pose a framework for assessing variation in a facet (or facets)of biodiversity (taxonomic, functional, or phylogenetic)across four spatial levels: whole river basin (gamma), amongregions (beta among), among sites within regions (betawithin), and within sites (alpha). Such a framework bringstogether the inventory and differentiation aspects of spatialbiodiversity (Jurasinski et al., 2009) and existing data setssourced from biodiversity monitoring or ‘river health’ pro-grams could be readily analysed by existing community-levelmethods (e.g. those described by Anderson et al., 2011).
(2) Concordance of biodiversity responses tohydrological mechanisms among multipleorganism groups
Ecohydrological research across spatial scales has dispropor-tionately targeted particular organism groups overall (e.g.macroinvertebrates, fish) or particular organism groups atspecific spatial components of biodiversity (e.g. a bias formacroinvertebrate biodiversity studies to focus on alpha andbeta biodiversity components at the expense of regional-scalediversity responses; Table S1, Supporting Information).There remains a significant gap in research quantifying how
patterns of freshwater biodiversity vary across spatial scalesin response to hydrology, particularly for amphibians, birds,microorganisms, and algae; Table S1, Supporting Informa-tion). Such knowledge gaps impede the ability to determinerobust generalisations or theory of biodiversity responses tohydrological regimes by way of formal meta-analyses thatare necessary for predicting broader biodiversity responsesto hydrological alterations.
Inevitably, biodiversity assessments are based on a subsetof organisms intended to serve as proxies (surrogates)for overall biodiversity, or on organisms of concernor significance. Cross-taxon congruency of biodiversityvariables is generally low (Westgate et al., 2014), suggestingthat a range of organism groups is necessary for quantifyingtrue biodiversity condition and responses to environmentalgradients (Heino, 2010). However, few studies compare theeffects of environmental gradients (particularly hydrologicalgradients) on different organism groups (e.g. invertebratesversus macrophytes versus fish) in freshwater ecosystems (e.g.Johnson et al., 2014). It is therefore not yet understoodhow well spatial biodiversity patterns of particularorganism groups (e.g. macroinvertebrates) reflect gradientsin broader multi-organism-group biodiversity patterns. Thisgap could be addressed by first investigating relationships ofhydrological gradients to different organism groups at thesame spatial scales to test assumptions of concordance acrossorganism groups, or if responses vary on the basis of organism
(e.g. dispersal) characteristics (e.g. Padial et al., 2014). Issuesof taxonomic surrogacy are important because monitoringprograms evaluating the performance of environmental flowsin biodiversity conservation across spatial scales are costlyto implement. Therefore, if a subset of organism groups isa reliable surrogate for broader biodiversity across differentspatial scales, this subset could be used to allocate monitoringresources to sampling more sites (or more frequently) ratherthan sampling multiple organism groups that show thesame hydrological responses. Such evidence would be ofsignificant value to conservation managers when designingcost-effective monitoring programs to assess the performanceof environmental flow programs and understanding howimpacts of hydrological alteration persist or vary over time.
(3) Multi-faceted biodiversity responses tohydrological regimes across spatial scales
Knowledge of the effects of hydrological regimes onfunctional and phylogenetic facets of biodiversity isrespectively limited and almost non-existent, therebyhindering our ability to predict effects of hydrological changeson ecosystem functioning and evolutionary potential.Furthermore, there is inconsistent evidence that alpha,beta and gamma components of taxonomic, functionaland phylogenetic diversity respond in the same way toenvironmental gradients in terrestrial systems (e.g. Meynardet al., 2011; Tobias & Monika, 2012; Arnan, Cerda & Retana,2017). Studies from terrestrial or marine systems suggestthat changes in taxonomic diversity may underestimatedeclines in functional and phylogenetic diversity (Baiser& Lockwood, 2011; D’agata et al., 2014). An improvedunderstanding of phylogenetic and functional responses tohydrology across spatial scales should begin with preliminarystudies examining how the different facets of biodiversityrespond to hydrological gradients across spatial scales forspecific organism groups. Numerous advances exist inanalytical methods and developments in frameworks foranalysing taxonomic, functional and phylogenetic diversitypatterns across spatial scales (e.g. Cardoso et al., 2014; Hui& McGeoch, 2014; Pavoine & Ricotta, 2014; Pavoine et al.,2016; Tucker et al., 2017) and these should be applied tosuitable new or existing freshwater biodiversity data setswhere complementary hydrological data are available andas details of organism traits become better understood(Chessman, 2015). Some studies have explored patternsof phylogenetic and functional biodiversity in freshwatersystems (e.g. Strecker et al., 2011; Blanchet et al., 2014; Heino& Tolonen, 2017), but none has explicitly tested how thesefacets vary in response to hydrology across spatial scales.
(4) Combined use of natural and anthropogenichydrological gradients to improve confidence inbiodiversity responses to hydrology
Outcomes of research examining biodiversity responses togradients in natural hydrology are frequently applied to pre-dicting consequences of anthropogenic changes in hydrology.
Dams alter hydrological regimes (e.g. Magilligan & Nislow,2005) thereby creating spatial anthropogenic gradients inhydrology (Mackay, Arthington & James, 2014), and anextensive literature focusses on the ecological consequencesof these changes (e.g. Poff & Zimmerman, 2010). Studiesof these ecological responses to hydrological regime changesinclude a strong emphasis on multi-species biodiversity, yetthe consequences for biodiversity are inadequately synthe-sised with frameworks of spatial scaling that have beenadopted by ecology and conservation biology in general.At least two potential approaches can address this defi-ciency. First, existing literature could be synthesised (orre-synthesised) to explore how different components of bio-diversity respond to anthropogenic hydrological gradients.Second, gaps in the existing literature could be filled by newstudies designed to assess effects of anthropogenic alterationof hydrological regimes across spatial scales. The combineduse of both natural and anthropogenic hydrological gradientscan both strengthen the ability to predict impacts of anthro-pogenic changes and identify underlying causal ecologicalmechanisms responsible for biodiversity patterns (Fukami &Wardle, 2005).
(5) Temporal change in spatial biodiversitypatterns
A consistent justification for research on the effects ofhydrology on freshwater biodiversity is that more evidenceis needed to predict future biodiversity condition in responseto direct (e.g. water-resource development) and indirect (e.g.climate change) effects of humans on hydrology. While suchpredictions are adopted by monitoring programs to assessthe consequences of such changes, they are also increasinglyadopted when designing field monitoring to assess the per-formance of environmental flow programs in achieving theirdesired targets of biodiversity conservation or restoration.However, it is still unclear whether particular spatial compo-nents of biodiversity are more responsive (i.e. respond morerapidly or clearly) to hydrological events or hydrologicalregime change than others. If particular spatial componentsof biodiversity respond rapidly to hydrological events (e.g.managed floodplain inundation), their identification wouldbe beneficial to designing monitoring programs with themost appropriate spatial grain and extent, and temporalfrequency and duration of sampling (sensu Downes, 2010).
Most studies of freshwater biodiversity responses to hydrol-ogy (and ecohydrological mechanisms) are based on datafrom single geographic regions representing specific climates,which in turn determine regional hydrological predictability.However, there is increasing combination or reuse of datasets from multiple climatic regions testing the effects ofhydrological events on freshwater biodiversity (e.g. Datryet al., 2014a) or comparing the effect of hydrology on freshwa-ter biodiversity at single spatial scales (e.g. Leigh et al., 2016).
Despite such broad-scale evidence, there remains a gap inunderstanding if effects of hydrological regimes and ecohy-drological mechanisms on spatial components of biodiversityare generalisable across regions with contrasting hydrolog-ical predictability driven by climate (Fig. 3). For example,climatic variation may partly explain inconsistencies in thedegree to which spatial variation in the taxonomic compo-sition of assemblages is driven by turnover or nestednessalong gradients of habitat persistence. Increasing emphasison cross-climate studies would be of considerable benefit todetermining the extent to which hydrology–biodiversity rela-tionships can be generalised and adopted in environmentalflow planning (sensu Poff et al., 2010).
VIII. CONCLUSIONS
(1) The highly dynamic and concentrated nature offreshwater biodiversity, combined with sustained demandsfor fresh water to satisfy human demands, means thatfreshwaters provide a unique and essential model system forunderstanding the mechanisms that determine how patternsof biodiversity vary across spatial scales.
(2) The hydrological regime of rivers, wetlands andfloodplains has long been viewed as the primary determinantof their biodiversity. Previous conceptualisations of therole of hydrology and syntheses of empirical evidence ofthe responses of biodiversity to hydrological change havenot adequately addressed the dependency of biodiversityon spatial scaling, or only focussed on the role of singleecohydrological mechanisms.
(3) Scale-dependent biodiversity responses to hydrologyare driven by different combinations of ecohydrologicalmechanisms operating at different spatial scales. Both habitatand disturbance mechanisms are major hydrological driversof regional (basin)-scale freshwater biodiversity (gammadiversity) and variation in biodiversity among landscapes.At smaller spatial scales, hydrological connectivity becomesincreasingly important as a driver of biodiversity, in terms ofboth spatial variation in composition (beta diversity withinriver networks) and local taxa richness (alpha diversity).Disturbance and habitat mechanisms linking hydrology andbiodiversity remain important from regional to local spatialscales.
(4) Importantly, hydrology has contrasting effects ondifferent spatial components of freshwater biodiversity.Recognising this contrast is critical because biodiversity atfine spatial scales may be positively influenced by hydrologi-cal gradients, whereas biodiversity at other spatial scales maydecline along the same hydrological gradient. This differenceemphasises that studies of responses of freshwater biodi-versity to hydrological regimes must adopt a multi-scaledapproach. However, simply increasing the spatial extent ofbiodiversity analysis does not address this issue.
(5) An overarching goal of freshwater conservation policiesworldwide is to sustain and restore freshwater biodiversity.Quantifying the true effects on freshwater biodiversity of
hydrological change by anthropogenic impacts and climatechange can be achieved only by integrating the responsesof different spatial components of biodiversity to hydrology.Studies or monitoring programs that evaluate the effectsof environmental flows on freshwater biodiversity but donot analyse responses in a multi-scaled context may missdetecting responses of biodiversity at specific spatial scales.
(6) We conclude that maximising the success andavoiding potential risks of environmental flow programsfor freshwater biodiversity are best addressed by identifyinghow ecohydrological mechanisms influence biodiversityat separate spatial scales. In addition, the responses ofbiodiversity to hydrological regimes across spatial scalesdepend on the biological and ecological characteristics offocal organism groups because there is a substantial degree ofinconsistency in hydrology–biodiversity relationships acrossdifferent organism groups.
(7) There is a major need to determine how functionaland phylogenetic facets of community-level biodiversity areinfluenced by hydrology to gain a stronger conceptualunderstanding of how hydrological change affects ecosystemfunctioning and the evolutionary capacity of biodiversity toadapt to further environmental changes.
(8) Our synthesis highlights significant gaps in the literatureof freshwater biodiversity responses to hydrology. These gapsstem from a poor uptake of concepts of spatial scaling infreshwater ecology that have been adopted by conservationecology more generally. Future research that addressesthese knowledge gaps will provide a stronger basis for themanagement of hydrological regimes to achieving tangiblebenefits for freshwater biodiversity.
IX. ACKNOWLEDGEMENTS
We thank Andrew Boulton and Barb Downes for reviewingdrafts of this manuscript and helpful discussions that helpedrefine the ideas presented here, and five referees for sharingtheir comments on a previous version of this manuscript,which stimulated many improvements to the final paper.
X. REFERENCES
References marked with asterisk have been cited within the supporting informationAcreman, M., Arthington, A. H., Colloff, M. J., Couch, C., Crossman, N.
D., Dyer, F., Overton, I., Pollino, C. A., Stewardson, M. J. & Young, W.(2014). Environmental flows for natural, hybrid, and novel riverine ecosystems in achanging world. Frontiers in Ecology and the Environment 12, 466–473.
Acreman, M. C. & Ferguson, A. J. D. (2010). Environmental flows and the Europeanwater framework directive. Freshwater Biology 55, 32–48.
*Adamek, Z., Konecna, J., Podhrazska, J., Vsetickova, L. & Juradova, Z.(2016). Response of small-stream biota to sudden flow pulses following extremeprecipitation events. Polish Journal of Environmental Studies 25, 495–501.
*Aguiar, F. C., Ferreira, M. T. & Albuquerque, A. (2006). Patterns of exotic andnative plant species richness and cover along a semi-arid Iberian river and across itsfloodplain. Plant Ecology 184, 189–202.
Akasaka, M. & Takamura, N. (2012). Hydrologic connection between pondspositively affects macrophyte α and γ diversity but negatively affects β diversity.Ecology 93, 967–973.
Alexandre, C. M., Ferreira, T. F. & Almeida, P. R. (2013). Fish assemblages innon-regulated and regulated rivers from permanent and temporary Iberian systems.River Research and Applications 29, 1042–1058.
Algarte, V., Siqueira, N., Murakami, E. & Rodrigues, L. (2009). Effects ofhydrological regime and connectivity on the interannual variation in taxonomicsimilarity of periphytic algae. Brazilian Journal of Biology 69, 609–616.
Almeida, B. D. A., Gimenes, M. R. & Dos Anjos, L. (2017). Wading bird functionaldiversity in a floodplain: Influence of habitat type and hydrological cycle. Austral
Ecology 42, 84–93.Amoros, C. & Bornette, G. (2002). Connectivity and biocomplexity in waterbodies
of riverine floodplains. Freshwater Biology 47, 761–776.Anderson, M. J., Crist, T. O., Chase, J. M., Vellend, M., Inouye, B. D.,
Freestone, A. L., Sanders, N. J., Cornell, H. V., Comita, L. S., Davies, K.F., Harrison, S. P., Kraft, N. J. B., Stegen, J. C. & Swenson, N. G. (2011).Navigating the multiple meanings of β diversity: a roadmap for the practicingecologist. Ecology Letters 14, 19–28.
Anderson, M. J., Ellingsen, K. E. & McArdle, B. H. (2006). Multivariatedispersion as a measure of beta diversity. Ecology Letters 9, 683–693.
Angermeier, P. L. (2010). Conservation challenges for stream fish ecologists. InCommunity Ecology of Stream Fishes: Concepts, Approaches, and Techniques (eds K. B. Gidoand D. A. Jackson). American Fisheries Society, Bethesda, PP: 303–310.
ARMCANZ & ANZECC (1996). National Principles for the Provision of Water forEcosystems. Occasional Paper SWR No. 3. ARMCANZ and ANZECC, Canberra,pp. 14.
Arnan, X., Cerda, X. & Retana, J. (2017). Relationships among taxonomic,functional, and phylogenetic ant diversity across the biogeographic regions ofEurope. Ecography 40, 448–457.
*Arscott, D. B., Larned, S., Scarsbrook, M. R. & Lambert, P. (2010). Aquaticinvertebrate community structure along an intermittence gradient: Selwyn River,New Zealand. Journal of the North American Benthological Society 29, 530–545.
Arthaud, F., Vallod, D., Robin, J. & Bornette, G. (2012). Eutrophication anddrought disturbance shape functional diversity and life-history traits of aquatic plantsin shallow lakes. Aquatic Sciences 74, 471–481.
Arthington, A. H. & Pusey, B. J. (2003). Flow restoration and protection inAustralian rivers. River Research and Applications 19, 377–395.
*Assis, R. L., Wittmann, F., Piedade, M. T. F. & Haugaasen, T. (2015). Effectsof hydroperiod and substrate properties on tree alpha diversity and composition inAmazonian floodplain forests. Plant Ecology 216, 41–54.
*Atkinson, C. L., Julian, J. P. & Vaughn, C. C. (2014). Species and function lost:role of drought in structuring stream communities. Biological Conservation 176, 30–38.
Baiser, B. & Lockwood, J. L. (2011). The relationship between functional andtaxonomic homogenization. Global Ecology and Biogeography 20, 134–144.
Baker, D. B., Richards, R. P., Loftus, T. T. & Kramer, J. W. (2004). A newflashiness index: characteristics and applications to midwestern rivers and streams.Journal of the American Water Resources Association 40, 503–522.
*Baldwin, D. S., Colloff, M. J., Rees, G. N., Chariton, A. A., Watson, G.O., Court, L. N., Hartley, D. M., Morgan, M. J., King, A. J., Wilson, J.S., Hodda, M. & Hardy, C. M. (2013). Impacts of inundation and drought oneukaryote biodiversity in semi-arid floodplain soils. Molecular Ecology 22, 1746–1758.
Baselga, A. (2010). Partitioning the turnover and nestedness components of betadiversity. Global Ecology and Biogeography 19, 134–143.
Beche, L. A., Connors, P. G., Resh, V. H. & Merenlender, A. M. (2009).Resilience of fishes and invertebrates to prolonged drought in two Californiastreams. Ecography 32, 778–788.
Beesley, L. S. & Prince, J. (2010). Fish community structure in an intermittent river:the importance of environmental stability, landscape factors and within-pool habitatdescriptors. Marine and Freshwater Research 61, 605–614.
*Beja, P., Santos, C. D., Santana, J., Pereira, M. J., Marques, J. T., Queiroz, H.L. & Palmeirim, J. M. (2010). Seasonal patterns of spatial variation in understorybird assemblages across a mosaic of flooded and unflooded Amazonian forests.Biodiversity and Conservation 19, 129–152.
Belmar, O., Velasco, J., Gutierrez-Canovas, C., Mellado-Díaz, A., Millan,A. & Wood, P. J. (2013). The influence of natural flow regimes on macroinvertebrateassemblages in a semiarid Mediterranean basin. Ecohydrology 6, 363–379.
Benke, A. C., Chaubey, I., Ward, G. M. & Dunn, E. L. (2000). Flood pulse dynamicsof an unregulated river floodplain in the southeastern U.S. coastal plain. Ecology 81,2730–2741.
Besemer, K., Singer, G., Hodl, I. & Battin, T. J. (2009). Bacterial communitycomposition of stream biofilms in spatially variable-flow environments. Applied and
Environmental Microbiology 75, 7189–7195.Bhamjee, R., Lindsay, J. B. & Cockburn, J. (2016). Monitoring ephemeral
headwater streams: a paired-sensor approach. Hydrological Processes 30, 888–898.Biggs, B. J. F., Nikora, V. L. & Snelder, T. H. (2005). Linking scales of flow
variability to lotic ecosystem structure and function. River Research and Applications 21,283–298.
Biggs, B. J. F. & Smith, R. A. (2002). Taxonomic richness of stream benthic algae:effects of flood disturbance and nutrients. Limnology and Oceanography 47, 1175–1186.
*Bini, L. M., Velho, L. F. M. & Lansac-Toha, F. A. (2003). The effect of connectivityon the relationship between local and regional species richness of testate amoebae(protozoa, rhizopoda) in floodplain lagoons of the Upper Parana River, Brazil. Acta
Oecologica-International Journal of Ecology 24, S145–S151.Blanchet, S., Helmus, M. R., Brosse, S. & Grenouillet, G. (2014). Regional
vs local drivers of phylogenetic and species diversity in stream fish communities.Freshwater Biology 59, 450–462.
Bogan, M. T., Boersma, K. S. & Lytle, D. A. (2013). Flow intermittency alterslongitudinal patterns of invertebrate diversity and assemblage composition in anarid-land stream network. Freshwater Biology 58, 1016–1028.
Bogan, M. T. & Lytle, D. A. (2011). Severe drought drives novel communitytrajectories in desert stream pools. Freshwater Biology 56, 2070–2081.
*Borics, G., Tothmeresz, B., Grigorszky, I., Padisak, J., Varbiro, G. & Szabo,S. (2003). Algal assemblage types of bog-lakes in Hungary and their relation to waterchemistry, hydrological conditions and habitat diversity. Hydrobiologia 502, 145–155.
Bornette, G., Amoros, C. & Lamouroux, N. (1998). Aquatic plant diversity inriverine wetlands: the role of connectivity. Freshwater Biology 39, 267–283.
*Bortolini, J. C., Train, S. & Rodrigues, L. C. (2016). Extreme hydrologicalperiods: effects on phytoplankton variability and persistence in a subtropicalfloodplain. Hydrobiologia 763, 223–236.
Boulton, A. J. (2003). Parallels and contrasts in the effect of drought on streammacroinvertebrate assemblages. Freshwater Biology 48, 1173–1185.
Boulton, A. J., Brock, M. A., Robson, B. J., Ryder, D. S., Chambers, J.M. & Davis, J. A. (2014). Australian Freshwater Ecology: Processes and Management.Wiley-Blackwell, Chichester.
*Boulton, A. J. & Stanley, E. H. (1995). Hyporheic processes during flooding anddrying in a Sonoran Desert stream. II. Faunal dynamics. Archiv Fur Hydrobiologie 134,27–52.
Brendonck, L., Jocque, M., Tuytens, K., Timms, B. V. & Vanschoenwinkel,B. (2015). Hydrological stability drives both local and regional diversity patterns inrock pool metacommunities. Oikos 124, 741–749.
Brock, M. A., Nielsen, D. L., Shiel, R. J., Green, J. D. & Langley, J. D. (2003).Drought and aquatic community resilience: the role of eggs and seeds in sedimentsof temporary wetlands. Freshwater Biology 48, 1207–1218.
*Budke, J. C., Jarenkow, J. A. & De Oliveira, A. T. (2008). Tree communityfeatures of two stands of riverine forest under different flooding regimes in SouthernBrazil. Flora 203, 162–174.
*Buendia, C., Gibbins, C. N., Vericat, D. & Batalla, R. J. (2014). Effects of flowand fine sediment dynamics on the turnover of stream invertebrate assemblages.Ecohydrology 7, 1105–1123.
Bunn, S. E. & Arthington, A. H. (2002). Basic principles and ecologicalconsequences of altered flow regimes for aquatic biodiversity. Environmental
Management 30, 492–507.Capon, S. J. (2005). Flood variability and spatial variation in plant community
composition and structure on a large arid floodplain. Journal of Arid Environments 60,283–302.
*Cardinale, B. J., Hillebrand, H. & Charles, D. F. (2006). Geographic patternsof diversity in streams are predicted by a multivariate model of disturbance andproductivity. Journal of Ecology 94, 609–618.
Cardinale, B. J., Palmer, M. A., Ives, A. R. & Brooks, S. S. (2005).Diversity-productivity relationships in streams vary as a function of the naturaldisturbance regime. Ecology 86, 716–726.
Cardoso, P., Rigal, F., Carvalho, J. C., Fortelius, M., Borges, P. A. V.,Podani, J. & Schmera, D. (2014). Partitioning taxon, phylogenetic and functionalbeta diversity into replacement and richness difference components. Journal of
Biogeography 41, 749–761.Carlisle, D. M., Wolock, D. M. & Meador, M. R. (2011). Alteration of streamflow
magnitudes and potential ecological consequences: a multiregional assessment.Frontiers in Ecology and the Environment 9, 264–270.
Carvalho, J. C., Cardoso, P. & Gomes, P. (2012). Determining the relative rolesof species replacement and species richness differences in generating beta-diversitypatterns. Global Ecology and Biogeography 21, 760–771.
Casanova, M. T. & Brock, M. A. (2000). How do depth, duration and frequencyof flooding influence the establishment of wetland plant communities? Plant Ecology
147, 237–250.Chakona, A., Phiri, C., Magadza, C. & Brendonck, L. (2008). The influence
of habitat structure and flow permanence on macroinvertebrate assemblages intemporary rivers in northwestern Zimbabwe. Hydrobiologia 607, 199–209.
*Chalmers, A. C., Erskine, W. D., Keene, A. F. & Bush, R. T. (2012). Relationshipbetween vegetation, hydrology and fluvial landforms on an unregulated sand-bedstream in the Hunter Valley, Australia. Austral Ecology 37, 193–203.
*Chappuis, E., Gacia, E. & Ballesteros, E. (2014). Environmental factorsexplaining the distribution and diversity of vascular aquatic macrophytes in ahighly heterogeneous Mediterranean region. Aquatic Botany 113, 72–82.
Chase, J. M. (2007). Drought mediates the importance of stochastic communityassembly. Proceedings of the Natural Academy of Sciences of the United States of America 104,17430–17434.
Chessman, B. C. (2015). Relationships between lotic macroinvertebrate traits andresponses to extreme drought. Freshwater Biology 60, 50–63.
Chessman, B. C. & Hardwick, L. (2014). Water regimes and macroinvertebrateassemblages in floodplain wetlands of the Murrumbidgee River, Australia. Wetlands
34, 661–672.Chester, E. T. & Robson, B. J. (2011). Drought refuges, spatial scale and
recolonisation by invertebrates in non-perennial streams. Freshwater Biology 56,2094–2104.
Chiarucci, A., Bacaro, G. & Scheiner, S. M. (2011). Old and new challenges inusing species diversity for assessing biodiversity. Philosophical Transactions of the Royal
Society of London B: Biological Sciences 366, 2426–2437.Clarke, A., Mac Nally, R., Bond, N. & Lake, P. S. (2010). Flow permanence affects
aquatic macroinvertebrate diversity and community structure in three headwaterstreams in a forested catchment. Canadian Journal of Fisheries and Aquatic Sciences 67,1649–1657.
Connell, J. H. (1978). Diversity in tropical rain forests and coral reefs. Science 199,1302–1310.
*Couto, A. P., Ferreira, E., Torres, R. T. & Fonseca, C. (2017). Local andlandscape drivers of pond-breeding amphibian diversity at the northern edge of theMediterranean. Herpetologica 73, 10–17.
D’agata, S., Mouillot, D., Kulbicki, M., Andrefouet, S., Bellwood, D. R.,Cinner, J. E., Cowman, P. F., Kronen, M., Pinca, S. & Vigliola, L. (2014).Human-mediated loss of phylogenetic and functional diversity in coral reef fishes.Current Biology 24, 555–560.
*Damasco, G., Vicentini, A., Castilho, C. V., Pimentel, T. P. & Nascimento,H. E. M. (2013). Disentangling the role of edaphic variability, flooding regimeand topography of Amazonian white-sand vegetation. Journal of Vegetation Science 24,384–394.
Datry, T. (2012). Benthic and hyporheic invertebrate assemblages along a flowintermittence gradient: effects of duration of dry events. Freshwater Biology 57,563–574.
Datry, T., Larned, S. T., Fritz, K. M., Bogan, M. T., Wood, P. J., Meyer,E. I. & Santos, A. N. (2014a). Broad-scale patterns of invertebrate richness andcommunity composition in temporary rivers: effects of flow intermittence. Ecography
37, 94–104.Datry, T., Corti, R. & Philippe, M. (2012). Spatial and temporal aquatic–terrestrial
transitions in the temporary Albarine River, France: responses of invertebrates toexperimental rewetting. Freshwater Biology 57, 716–727.
*Datry, T., Corti, R., Belletti, B. & Piegay, H. (2014b). Ground-dwellingarthropod communities across braided river landscape mosaics: a Mediterraneanperspective. Freshwater Biology 59, 1308–1322.
Datry, T., Larned, S. T. & Scarsbrook, M. R. (2007). Responses ofhyporheic invertebrate assemblages to large-scale variation in flow permanenceand surface-subsurface exchange. Freshwater Biology 52, 1452–1462.
*Datry, T., Melo, A. S., Moya, N., Zubieta, J., De La Barra, E. & Oberdorff,T. (2016). Metacommunity patterns across three Neotropical catchments withvarying environmental harshness. Freshwater Biology 61, 277–292.
Davey, A. J. H. & Kelly, D. J. (2007). Fish community responses to drying disturbancesin an intermittent stream: a landscape perspective. Freshwater Biology 52, 1719–1733.
Davidson, T. A., Mackay, A. W., Wolski, P., Mazebedi, R., Murray-Hudson,M. & Todd, M. (2012). Seasonal and spatial hydrological variability drives aquaticbiodiversity in a flood-pulsed, sub-tropical wetland. Freshwater Biology 57, 1253–1265.
Davies, P. E., Harris, J. H., Hillman, T. J. & Walker, K. F. (2010). TheSustainable Rivers Audit: assessing river ecosystem health in the Murray–DarlingBasin, Australia. Marine and Freshwater Research 61, 764–777.
Davies, P. M., Naiman, R. J., Warfe, D. M., Pettit, N. E., Arthington, A.H. & Bunn, S. E. (2014). Flow–ecology relationships: closing the loop on effectiveenvironmental flows. Marine and Freshwater Research 65, 133–141.
*De Jager, N. R., Rohweder, J. J., Yin, Y. & Hoy, E. (2016). The UpperMississippi River floodscape: spatial patterns of flood inundation and associatedplant community distributions. Applied Vegetation Science 19, 164–172.
Death, R. G. & Winterbourn, M. J. (1995). Diversity patterns in stream benthicinvertebrate communities: the influence of habitat stability. Ecology 76, 1446–1460.
Death, R. G. & Zimmermann, E. M. (2005). Interaction between disturbanceand primary productivity in determining stream invertebrate diversity. Oikos 111,392–402.
Della Bella, V., Bazzanti, M. & Chiarotti, F. (2005). Macroinvertebratediversity and conservation status of Mediterranean ponds in Italy: water permanenceand mesohabitat influence. Aquatic Conservation: Marine and Freshwater Ecosystems 15,583–600.
Detenbeck, N. E., Brady, V. J., Taylor, D. L., Snarski, V. M. & Batterman,S. L. (2005). Relationship of stream flow regime in the western Lake Superior basinto watershed type characteristics. Journal of Hydrology 309, 258–276.
Devictor, V., Mouillot, D., Meynard, C., Jiguet, F., Thuiller, W. &Mouquet, N. (2010). Spatial mismatch and congruence between taxonomic,phylogenetic and functional diversity: the need for integrative conservation strategiesin a changing world. Ecology Letters 13, 1030–1040.
Dewson, Z. S., James, A. B. W. & Death, R. G. (2007). A review of the consequencesof decreased flow for instream habitat and macroinvertebrates. Journal of the North
American Benthological Society 26, 401–415.*Dos Santos, A. M. & Thomaz, S. M. (2007). Aquatic macrophytes diversity in
lagoons of a tropical floodplain: the role of connectivity and water level. Austral
Ecology 32, 177–190.Downes, B. J. (2010). Back to the future: little-used tools and principles of scientific
inference can help disentangle effects of multiple stressors on freshwater ecosystems.Freshwater Biology 55, 60–79.
*Driver, L. J. & Hoeinghaus, D. J. (2016). Spatiotemporal dynamics of intermittentstream fish metacommunities in response to prolonged drought and reconnectivity.Marine and Freshwater Research 67, 1667–1679.
Dudgeon, D., Arthington, A. H., Gessner, M. O., Kawabata, Z.-I., Knowler,D. J., Eacute, E., Que, C., Naiman, R. J., Prieur-Richard, A.-H., Egrave, N.,Soto, D., Stiassny, M. L. J. & Sullivan, C. A. (2006). Freshwater biodiversity:importance, threats, status and conservation challenges. Biological Reviews 81,163–182.
Edge, C. B., Fortin, M.-J., Jackson, D. A., Lawrie, D., Stanfield, L. &Shrestha, N. (2017). Habitat alteration and habitat fragmentation differentiallyaffect beta diversity of stream fish communities. Landscape Ecology 32, 647–662.
*Escalera-Vazquez, L. H. & Zambrano, L. (2010). The effect of seasonal variationin abiotic factors on fish community structure in temporary and permanent pools ina tropical wetland. Freshwater Biology 55, 2557–2569.
Euliss, N. H., Labaugh, J. W., Fredrickson, L. H., Mushet, D. M., Laubhan,M. K., Swanson, G. A., Winter, T. C., Rosenberry, D. O. & Nelson, R. D.(2004). The wetland continuum: a conceptual framework for interpreting biologicalstudies. Wetlands 24, 448–458.
Faith, D. P. (1992). Conservation evaluation and phylogenetic diversity. Biological
Conservation 61, 1–10.Fausch, K. D., Torgersen, C. E., Baxter, C. V. & Li, H. W. (2002). Landscapes
to riverscapes: bridging the gap between research and conservation of stream fishes.BioScience 52, 483–498.
Fazi, S., Vazquez, E., Casamayor, E. O., Amalfitano, S. & Butturini, A.(2013). Stream hydrological fragmentation drives bacterioplankton communitycomposition. PLoS ONE 8, e64109.
*Febria, C. M., Beddoes, P., Fulthorpe, R. R. & Williams, D. D. (2012).Bacterial community dynamics in the hyporheic zone of an intermittent stream.ISME Journal 6, 1078–1088.
Feminella, J. W. (1996). Comparison of benthic macroinvertebrate assemblages insmall streams along a gradient of flow permanence. Journal of the North American
Benthological Society 15, 651–669.Fernandes, R., Gomes, L. C., Pelicice, F. M. & Agostinho, A. A. (2009).
Temporal organization of fish assemblages in floodplain lagoons: the role ofhydrological connectivity. Environmental Biology of Fishes 85, 99–108.
*Ferreira, L. V. & Stohlgren, T. J. (1999). Effects of river level fluctuation onplant species richness, diversity, and distribution in a floodplain forest in CentralAmazonia. Oecologia 120, 582–587.
*Fitzgerald, D. B., Winemiller, K. O., Sabaj Perez, M. H. & Sousa, L.M. (2017). Seasonal changes in the assembly mechanisms structuring tropical fishcommunities. Ecology 98, 21–31.
*Foulquier, A., Dehedin, A., Piscart, C., Montuelle, B. & Marmonier, P.(2014). Habitat heterogeneity influences the response of microbial communities tosevere low-flow periods in alluvial wetlands. Freshwater Biology 59, 463–476.
Fraisse, S., Bormans, M. & Lagadeuc, Y. (2013). Morphofunctional traits reflectdifferences in phytoplankton community between rivers of contrasting flow regime.Aquatic Ecology 47, 315–327.
Freedman, J. A., Lorson, B. D., Taylor, R. B., Carline, R. F. & Stauffer,J. R. Jr. (2014). River of the dammed: longitudinal changes in fish assemblages inresponse to dams. Hydrobiologia 727, 19–33.
Frissell, C. A., Liss, W. J., Warren, C. E. & Hurley, M. D. (1986). A hierarchicalframework for stream habitat classification: viewing streams in a watershed context.Environmental Management 10, 199–214.
Fritz, K. M. & Dodds, W. K. (2005). Harshness: characterisation of intermittentstream habitat over space and time. Marine and Freshwater Research 56, 13–23.
*Frutos, S. M., De Neiff, A. & Neiff, J. J. (2006). Zooplankton of theParaguay River: a comparison between sections and hydrological phases. Annales De
Limnologie-International Journal of Limnology 42, 277–288.Fukami, T. & Wardle, D. A. (2005). Long-term ecological dynamics: reciprocal
insights from natural and anthropogenic gradients. Proceedings of the Royal Society of
London Series B 272, 2105–2115.Gallardo, B., Doledec, S., Paillex, A., Arscott, D. B., Sheldon, F., Zilli,
F., Merigoux, S., Castella, E. & Comin, F. A. (2014). Response of benthicmacroinvertebrates to gradients in hydrological connectivity: a comparison oftemperate, subtropical, Mediterranean and semiarid river floodplains. Freshwater
Biology 59, 630–648.*Galle, R. & Schweger, S. (2014). Habitat and landscape attributes influencing
spider assemblages at lowland forest river valley (Hungary). North-Western Journal of
Garcia-Roger, E. M., Del Mar Sanchez-Montoya, M., Cid, N., Erba, S.,Karaouzas, I., Verkaik, I., Rieradevall, M., Gomez, R., Luisa Suarez, M.,Rosario Vidal-Abarca, M., Demartini, D., Buffagni, A., Skoulikidis, N.,Bonada, N. & Prat, N. (2013). Spatial scale effects on taxonomic and biologicaltrait diversity of aquatic macroinvertebrates in Mediterranean streams. Fundamental
and Applied Limnology 183, 89–105.Gaston, K. J. (1996). Biodiversity: A Biology of Numbers and Difference. Blackwell Science,
Cambridge.Gaston, K. J. & Spicer, J. I. (1998). Biodiversity: An Introduction. Blackwell Science,
Oxford, United Kingdom.*Giam, X., Chen, W., Schriever, T. A., Van Driesche, R., Muneepeerakul,
R., Lytle, D. A. & Olden, J. D. (2017). Hydrology drives seasonal variation indryland stream macroinvertebrate communities. Aquatic Sciences 79, 705–717.
Gomes, L., Bulla, C., Agostinho, A., Vasconcelos, L. & Miranda, L.(2012). Fish assemblage dynamics in a Neotropical floodplain relative to aquaticmacrophytes and the homogenizing effect of a flood pulse. Hydrobiologia 685, 97–107.
Gordon, N. D., McMahon, T., Finlayson, B. L., Gippel, C. J. & Nathan, R.J. (2004). Stream Hydrology: An Introduction for Ecologists, 2nd Edition (John Wiley andSons, Ltd, Chichester.
Graham, C. H. & Fine, P. V. A. (2008). Phylogenetic beta diversity: linking ecologicaland evolutionary processes across space in time. Ecology Letters 11, 1265–1277.
Greenwood, M. J. & Booker, D. J. (2015). The influence of antecedent floods onaquatic invertebrate diversity, abundance and community composition. Ecohydrology
8, 188–203.Griffiths, D. (2010). Pattern and process in the distribution of North American
freshwater fish. Biological Journal of the Linnean Society 100, 46–61.*Grubbs, S. (2011). Influence of flow permanence on headwater macroinvertebrate
communities in a Cumberland Plateau watershed, USA. Aquatic Ecology 45, 185–195.Hamilton, A. J. (2005). Species diversity or biodiversity? Journal of Environmental
Management 75, 89–92.Hart, D. D. & Finelli, C. M. (1999). Physical-biological coupling in streams: the
pervasive effects of flow on benthic organisms. Annual Review of Ecology and Systematics
30, 363–395.Hassall, C., Hollinshead, J. & Hull, A. (2011). Environmental correlates of plant
and invertebrate species richness in ponds. Biodiversity and Conservation 20, 3189–3222.Heino, J. (2010). Are indicator groups and cross-taxon congruence useful for predicting
biodiversity in aquatic ecosystems? Ecological Indicators 10, 112–117.Heino, J. (2011). A macroecological perspective of diversity patterns in the freshwater
realm. Freshwater Biology 56, 1703–1722.Heino, J., Melo, A. S. & Bini, L. M. (2015). Reconceptualising the beta
diversity-environmental heterogeneity relationship in running water systems.Freshwater Biology 60, 223–235.
Heino, J. & Tolonen, K. T. (2017). Ecological drivers of multiple facets of betadiversity in a lentic macroinvertebrate metacommunity. Limnology and Oceanography.In press.
Horrigan, N. & Baird, D. J. (2008). Trait patterns of aquatic insects across gradientsof flow-related factors: a multivariate analysis of Canadian national data. Canadian
Journal of Fisheries and Aquatic Sciences 65, 670–680.Hui, C. & McGeoch, M. A. (2014). Zeta diversity as a concept and metric that unifies
incidence-based biodiversity patterns. The American Naturalist 184, 684–694.Iwasaki, Y., Ryo, M., Sui, P. & Yoshimura, C. (2012). Evaluating the relationship
between basin-scale fish species richness and ecologically relevant flow characteristicsin rivers worldwide. Freshwater Biology 57, 2173–2180.
*Jacquemin, S. J. & Pyron, M. (2011). Impacts of past glaciation events oncontemporary fish assemblages of the Ohio River basin. Journal of Biogeography 38,982–991.
*James, C. S., Capon, S. J., White, M. G., Rayburg, S. C. & Thoms, M. C. (2007).Spatial variability of the soil seed bank in a heterogeneous ephemeral wetland systemin semi-arid Australia. Plant Ecology 190, 205–217.
*Jansson, R., Laudon, H., Johansson, E. & Augspurger, C. (2007). Theimportance of groundwater discharge for plant species number in riparian zones.Ecology 88, 131–139.
Jardine, T. D., Bond, N. R., Burford, M. A., Kennard, M. J., Ward, D. P.,Bayliss, P., Davies, P. M., Douglas, M. M., Hamilton, S. K., Melack, J.M., Naiman, R. J., Pettit, N. E., Pusey, B. J., Warfe, D. M. & Bunn, S. E.(2015). Does flood rhythm drive ecosystem responses in tropical riverscapes? Ecology
96, 684–692.Jarzyna, M. A. & Jetz, W. (2016). Detecting the multiple facets of biodiversity. Trends
in Ecology & Evolution 31, 527–538.*Jenkins, K. M. & Boulton, A. J. (2003). Connectivity in a dryland river: short-term
aquatic microinvertebrate recruitment following floodplain inundation. Ecology 84,2708–2723.
Johnson, R., Angeler, D., Moe, S. J. & Hering, D. (2014). Cross-taxonresponses to elevated nutrients in European streams and lakes. Aquatic Sciences
76, 51–60.*Johnson, S. E., Amatangelo, K. L., Townsend, P. A. & Waller, D. M. (2016).
Large, connected floodplain forests prone to flooding best sustain plant diversity.Ecology 97, 3019–3030.
Jurasinski, G., Retzer, V. & Beierkuhnlein, C. (2009). Inventory, differentiation,and proportional diversity: a consistent terminology for quantifying species diversity.Oecologia 159, 15–26.
Katz, G. L., Denslow, M. W. & Stromberg, J. C. (2012). The Goldilockseffect: intermittent streams sustain more plant species than those with perennial orephemeral flow. Freshwater Biology 57, 467–480.
*Kennard, M. J., Olden, J. D., Arthington, A. H., Pusey, B. J. & Poff, N.L. (2007). Multiscale effects of flow regime and habitat and their interaction onfish assemblage structure in eastern Australia. Canadian Journal of Fisheries and Aquatic
Sciences 64, 1346–1359.Keruzore, A. A., Willby, N. J. & Gilvear, D. J. (2013). The role of lateral
connectivity in the maintenance of macrophyte diversity and production in largerivers. Aquatic Conservation: Marine and Freshwater Ecosystems 23, 301–315.
*Kiflawi, M., Eitam, A. & Blaustein, L. (2003). The relative impact of localand regional processes on macro-invertebrate species richness in temporary pools.Journal of Animal Ecology 72, 447–452.
Kingsford, R. T., Jenkins, K. M. & Porter, J. L. (2004). Imposed hydrologicalstability on lakes in arid Australia and effects on waterbirds. Ecology 85,2478–2492.
Konrad, C. P., Brasher, A. M. D. & May, J. T. (2008). Assessing streamflowcharacteristics as limiting factors on benthic invertebrate assemblages in streamsacross the western United States. Freshwater Biology 53, 1983–1998.
*Kuglerova, L., Jansson, R., Agren, A., Laudon, H. & Malm-Renofalt, B.(2014). Groundwater discharge creates hotspots of riparian plant species richness ina boreal forest stream network. Ecology 95, 715–725.
*Kurzatkowski, D., Leuschner, C. & Homeier, J. (2015). Effects of flooding ontrees in the semi-deciduous transition forests of the Araguaia floodplain, Brazil. Acta
Oecologica-International Journal of Ecology 69, 21–30.Lake, P. S. (2000). Disturbance, patchiness, and diversity in streams. Journal of the North
American Benthological Society 19, 573–592.Lake, P. S. (2003). Ecological effects of perturbation by drought in flowing waters.
Freshwater Biology 48, 1161–1172.Lamouroux, N., Poff, N. L. & Angermeier, P. L. (2002). Intercontinental
convergence of stream fish community traits along geomorphic and hydraulicgradients. Ecology 83, 1792–1807.
*Lansac-Toha, F. M., Meira, B. R., Segovia, B. T., Lansac-Toha, F. A. &Velho, L. F. M. (2016). Hydrological connectivity determining metacommunitystructure of planktonic heterotrophic flagellates. Hydrobiologia 781, 81–94.
Larimore, R. W., Childers, W. F. & Heckrotte, C. (1959). Destruction andre-establishment of stream fish and invertebrates affected by drought. Transactions of
the American Fisheries Society 88, 261–285.Larned, S. T., Arscott, D. B., Schmidt, J. & Diettrich, J. C. (2010). A
framework for analyzing longitudinal and temporal variation in river flow anddeveloping flow-ecology relationships. Journal of the American Water Resources Association
46, 541–553.Larned, S. T., Datry, T., Arscott, D. B. & Tockner, K. (2010). Emerging
concepts in temporary-river ecology. Freshwater Biology 55, 717–738.Larned, S. T., Schmidt, J., Datry, T., Konrad, C. P., Dumas, J. K. & Diettrich,
J. C. (2011). Longitudinal river ecohydrology: flow variation down the lengths ofalluvial rivers. Ecohydrology 4, 532–548.
*Laske, S. M., Haynes, T. B., Rosenberger, A. E., Koch, J. C., Wipfli, M.S., Whitman, M. & Zimmerman, C. E. (2016). Surface water connectivity drivesrichness and composition of Arctic lake fish assemblages. Freshwater Biology 61,1090–1104.
Lasne, E., Lek, S. & Laffaille, P. (2007). Patterns in fish assemblages in the Loirefloodplain: the role of hydrological connectivity and implications for conservation.Biological Conservation 139, 258–268.
Lawson, J. R., Fryirs, K. A., Lenz, T. & Leishman, M. R. (2015). Heterogeneousflows foster heterogeneous assemblages: relationships between functional diversityand hydrological heterogeneity in riparian plant communities. Freshwater Biology 60,2208–2225.
Ledger, M., Harris, R., Armitage, P. & Milner, A. (2008). Disturbance frequencyinfluences patch dynamics in stream benthic algal communities. Oecologia 155,809–819.
Legendre, P. (2014). Interpreting the replacement and richness difference componentsof beta diversity. Global Ecology and Biogeography 23, 1324–1334.
Legendre, P. & De Caceres, M. (2013). Beta diversity as the variance of communitydata: dissimilarity coefficients and partitioning. Ecology Letters 16, 951–963.
Leigh, C., Bonada, N., Boulton, A. J., Hugueny, B., Larned, S. T., Vorste,R. & Datry, T. (2016). Invertebrate assemblage responses and the dual rolesof resistance and resilience to drying in intermittent rivers. Aquatic Sciences 78,291–301.
Leigh, C. & Datry, T. (2017). Drying as a primary hydrological determinant ofbiodiversity in river systems: a broad-scale analysis. Ecography 40, 487–499.
Leigh, C. & Sheldon, F. (2009). Hydrological connectivity drives patterns ofmacroinvertebrate biodiversity in floodplain rivers of the Australian wet/ drytropics. Freshwater Biology 54, 549–571.
*Leigh, C., Stubbington, R., Sheldon, F. & Boulton, A. J. (2013).Hyporheic invertebrates as bioindicators of ecological health in temporary rivers: ameta-analysis. Ecological Indicators 32, 62–73.
Leira, M. & Cantonati, M. (2008). Effects of water-level fluctuations on lakes: anannotated bibliography. Hydrobiologia 613, 171–184.
Lepori, F. & Hjerdt, N. (2006). Disturbance and aquatic biodiversity: reconcilingcontrasting views. Bioscience 56, 809–818.
Levin, S. A. (1992). The problem of pattern and scale in ecology: the Robert H.MacArthur Award Lecture. Ecology 73, 1943–1967.
Li, D. & Waller, D. (2015). Drivers of observed biotic homogenization in pinebarrens of central Wisconsin. Ecology 96, 1030–1041.
*Lind, P. R., Robson, B. J. & Mitchell, B. D. (2006). The influence of reduced flowduring a drought on patterns of variation in macroinvertebrate assemblages acrossa spatial hierarchy in two lowland rivers. Freshwater Biology 51, 2282–2295.
*Lopes, P. M., Bini, L. M., Declerck, S. A. J., Farjalla, V. F., Vieira, L. C.G., Bonecker, C. C., Lansac-Toha, F. A., Esteves, F. A. & Bozelli, R. L.(2014). Correlates of zooplankton beta diversity in tropical lake systems. PLoS ONE
9, e109581.Lougheed, V. L., McIntosh, M. D., Parker, C. A. & Stevenson, R. J. (2008).
Wetland degradation leads to homogenization of the biota at local and landscapescales. Freshwater Biology 53, 2402–2413.
Macedo-Soares, P. H. M. D., Petry, A. C., Farjalla, V. F. & Caramaschi,E. P. (2010). Hydrological connectivity in coastal inland systems: lessons from aNeotropical fish metacommunity. Ecology of Freshwater Fish 19, 7–18.
Mackay, S. J., Arthington, A. H. & James, C. S. (2014). Classification andcomparison of natural and altered flow regimes to support an Australian trial of theEcological Limits of Hydrologic Alteration framework. Ecohydrology 7, 1485–1507.
Magilligan, F. J. & Nislow, K. H. (2005). Changes in hydrologic regime by dams.Geomorphology 71, 61–78.
Magurran, A. E. (2004). Measuring Biological Diversity. Blackwell Publishing, Oxford.*Maltchik, L., Lanes, L. E. K., Stenert, C. & Medeiros, E. S. F. (2010).
Species-area relationship and environmental predictors of fish communities incoastal freshwater wetlands of southern Brazil. Environmental Biology of Fishes 88,25–35.
Marchetti, M. P., Esteban, E., Smith, A. N. H., Pickard, D., Richards, A. B. &Slusark, J. (2011). Measuring the ecological impact of long-term flow disturbanceon the macroinvertebrate community in a large Mediterranean climate river. Journal
of Freshwater Ecology 26, 459–480.*Marcogliese, D. J., Gendron, A. D. & Cone, D. K. (2009). Impact of municipal
effluents and hydrological regime on myxozoan parasite communities of fish.International Journal for Parasitology 39, 1345–1351.
*Marques, M. C. M., Burslem, D., Britez, R. M. & Silva, S. M. (2009). Dynamicsand diversity of flooded and unflooded forests in a Brazilian Atlantic rain forest: a16-year study. Plant Ecology & Diversity 2, 57–64.
*Marshall, J. C., Sheldon, F., Thoms, M. & Choy, S. (2006). Themacroinvertebrate fauna of an Australian dryland river: spatial and temporalpatterns and environmental relationships. Marine and Freshwater Research 57,61–74.
McCargo, J. W. & Peterson, J. T. (2010). An evaluation of the influence ofseasonal base flow and geomorphic stream characteristics on Coastal Plain streamfish assemblages. Transactions of the American Fisheries Society 139, 29–48.
*McCluney, K. E. & Sabo, J. L. (2012). River drying lowers the diversity and altersthe composition of an assemblage of desert riparian arthropods. Freshwater Biology
57, 91–103.McCune, J. L. & Vellend, M. (2013). Gains in native species promote biotic
homogenization over four decades in a human-dominated landscape. Journal of
Ecology 101, 1542–1551.McGarvey, D. J. (2014). Moving beyond species-discharge relationships to a
flow-mediated, macroecological theory of fish species richness. Freshwater Science
33, 18–31.McGarvey, D. J. & Terra, B. D. F. (2016). Using river discharge to model and
deconstruct the latitudinal diversity gradient for fishes of the Western Hemisphere.Journal of Biogeography 43, 1436–1449.
McGill, B. J., Dornelas, M., Gotelli, N. J. & Magurran, A. E. (2015). Fifteenforms of biodiversity trend in the Anthropocene. Trends in Ecology & Evolution 30,104–113.
McHugh, P. A., Thompson, R. M., Greig, H. S., Warburton, H. J. & McIntosh,A. R. (2015). Habitat size influences food web structure in drying streams. Ecography
38, 700–712.McKinney, M. L. & Lockwood, J. L. (1999). Biotic homogenization: a few winners
replacing many losers in the next mass extinction. Trends in Ecology & Evolution 14,450–453.
McManamay, R. A., Bevelhimer, M. S. & Frimpong, E. A. (2015). Associationsamong hydrologic classifications and fish traits to support environmental flowstandards. Ecohydrology 8, 460–479.
McManamay, R. A. & Frimpong, E. A. (2015). Hydrologic filtering of fish life historystrategies across the United States: implications for stream flow alteration. Ecological
Applications 25, 243–263.
McManamay, R. A., Orth, D. J. & Dolloff, C. A. (2012). Revisiting thehomogenization of dammed rivers in the southeastern US. Journal of Hydrology
424–425, 217–237.McMullen, L. E. & Lytle, D. A. (2012). Quantifying invertebrate resistance to
floods: a global-scale meta-analysis. Ecological Applications 22, 2164–2175.Meynard, C. N., Devictor, V., Mouillot, D., Thuiller, W., Jiguet, F. &
Mouquet, N. (2011). Beyond taxonomic diversity patterns: how do α, β and γ
components of bird functional and phylogenetic diversity respond to environmentalgradients across France? Global Ecology and Biogeography 20, 893–903.
*Miller, A. C. & Payne, B. S. (1998). Effects of disturbances on large-river musselassemblages. Regulated Rivers-Research & Management 14, 179–190.
Mims, M. C. & Olden, J. D. (2012). Life history theory predicts fish assemblageresponse to hydrologic regimes. Ecology 93, 35–45.
*Mouw, J. E. B., Stanford, J. A. & Alaback, P. B. (2009). Influences of floodingand hyporheic exchange on floodplain plant richness and productivity. River Research
and Applications 25, 929–945.*Murray-Hudson, M., Wolski, P., Murray-Hudson, F., Brown, M. T. &
Kashe, K. (2014). Disaggregating hydroperiod: components of the seasonal floodpulse as drivers of plant species distribution in of a tropical wetland. Wetlands 34,927–942.
*Mustonen, K.-R., Mykra, H., Marttila, H., Haghighi, A. T., Kløve, B.,Aroviita, J., Veijalainen, N., Sippel, K. & Muotka, T. (2016). Defining thenatural flow regimes of boreal rivers: relationship with benthic macroinvertebratecommunities. Freshwater Science 35, 559–572.
Nielsen, D., Podnar, K., Watts, R. J. & Wilson, A. L. (2013). Empirical evidencelinking increased hydrologic stability with decreased biotic diversity within wetlands.Hydrobiologia 708, 81–96.
Niu, S. Q., Franczyk, M. P. & Knouft, J. H. (2012). Regional species richness,hydrological characteristics and the local species richness of assemblages of NorthAmerican stream fishes. Freshwater Biology 57, 2367–2377.
Oberdorff, T., Guegan, J.-F. & Hugueny, B. (1995). Global scale patterns of fishspecies richness in rivers. Ecography 18, 345–352.
*O’Dea, C. B. (2014). The relationship between coastal plain pondvegetation and environment at local and broad spatial scales. Rhodora 116,187–223.
Olden, J. D., Kennard, M. J., Leprieur, F., Tedesco, P. A., Winemiller, K. O.& García-Berthou, E. (2010). Conservation biogeography of freshwater fishes:recent progress and future challenges. Diversity and Distributions 16, 496–513.
Olden, J. D., Konrad, C. P., Melis, T. S., Kennard, M. J., Freeman, M. C., Mims,M. C., Bray, E. N., Gido, K. B., Hemphill, N. P., Lytle, D. A., Mcmullen, L.E., Pyron, M., Robinson, C. T., Schmidt, J. C. & Williams, J. G. (2014). Arelarge-scale flow experiments informing the science and management of freshwaterecosystems? Frontiers in Ecology and the Environment 12, 176–185.
Olden, J. D. & Rooney, T. P. (2006). On defining and quantifying biotichomogenization. Global Ecology and Biogeography 15, 113–120.
*Padial, A. A., Carvalho, P., Thomaz, S. M., Boschilia, S. M., Rodrigues,R. B. & Kobayashi, J. T. (2009). The role of an extreme flood disturbanceon macrophyte assemblages in a Neotropical floodplain. Aquatic Sciences 71,389–398.
Padial, A. A., Ceschin, F., Declerck, S. A. J., De Meester, L., Bonecker, C. C.,Lansac-Toha, F. A., Rodrigues, L., Rodrigues, L. C., Train, S., Velho, L.F. M. & Bini, L. M. (2014). Dispersal ability determines the role of environmental,spatial and temporal drivers of metacommunity structure. PLoS ONE 9, e111227.
Paillex, A., Doledec, S., Castella, E., Merigoux, S. & Aldridge, D. C. (2013).Functional diversity in a large river floodplain: anticipating the response of nativeand alien macroinvertebrates to the restoration of hydrological connectivity. Journal
of Applied Ecology 50, 97–106.Palmer, M. A., Menninger, H. L. & Bernhardt, E. (2010). River restoration,
habitat heterogeneity and biodiversity: a failure of theory or practice? Freshwater
Biology 55, 205–222.Palmer, M. A., Reidy Liermann, C. A., Nilsson, C., Florke, M., Alcamo,
J., Lake, P. S. & Bond, N. (2008). Climate change and the world’s river basins:anticipating management options. Frontiers in Ecology and the Environment 6, 81–89.
*Pasquaud, S., Vasconcelos, R. P., Franca, S., Henriques, S., Costa, M. J.& Cabral, H. (2015). Worldwide patterns of fish biodiversity in estuaries: effect ofglobal vs. local factors. Estuarine Coastal and Shelf Science 154, 122–128.
Passy, S. I. & Blanchet, F. G. (2007). Algal communities in human-impacted streamecosystems suffer beta-diversity decline. Diversity and Distributions 13, 670–679.
Pavoine, S. & Bonsall, M. B. (2011). Measuring biodiversity to explain communityassembly: a unified approach. Biological Reviews 86, 792–812.
Pavoine, S., Marcon, E. & Ricotta, C. (2016). ’Equivalent numbers’ for species,phylogenetic or functional diversity in a nested hierarchy of multiple scales. Methods
in Ecology and Evolution 7, 1152–1163.Pavoine, S. & Ricotta, C. (2014). Functional and phylogenetic similarity among
communities. Methods in Ecology and Evolution 5, 666–675.Pegg, M. A. & Taylor, R. M. (2007). Fish species diversity among spatial scales of
altered temperate rivers. Journal of Biogeography 34, 549–558.
Penha, J., Landeiro, V. L., Ortega, J. C. G. & Mateus, L. (2017).Interchange between flooding and drying, and spatial connectivity control thefish metacommunity structure in lakes of the Pantanal wetland. Hydrobiologia 797,115–126.
Perkin, J. S., Gido, K. B., Cooper, A. R., Turner, T. F., Osborne, M. J.,Johnson, E. R. & Mayes, K. B. (2015). Fragmentation and dewatering transformGreat Plains stream fish communities. Ecological Monographs 85, 73–92.
Petchey, O. L. & Gaston, K. J. (2006). Functional diversity: back to basics andlooking forward. Ecology Letters 9, 741–758.
Pettit, N. E., Froend, R. H. & Davies, P. M. (2001). Identifying the natural flowregime and the relationship with riparian vegetation for two contrasting westernAustralian rivers. Regulated Rivers: Research & Management 17, 201–215.
Poff, N. L. (1992). Why disturbances can be predictable: a perspective on the definitionof disturbance in streams. Journal of the North American Benthological Society 11, 86–92.
Poff, N. L. & Allan, J. D. (1995). Functional organization of stream fish assemblagesin relation to hydrological variability. Ecology 76, 606–627.
Poff, N. L., Allan, J. D., Bain, M. B., Karr, J. R., Prestegaard, K. L., Richter,B. D., Sparks, R. E. & Stromberg, J. C. (1997). The natural flow regime. Bioscience
47, 769–784.Poff, N. L., Bledsoe, B. P. & Cuhaciyan, C. O. (2006). Hydrologic variation
with land use across the contiguous United States: geomorphic and ecologicalconsequences for stream ecosystems. Geomorphology 79, 264–285.
Poff, N. L. & Matthews, J. H. (2013). Environmental flows in the Anthropocene:past progress and future prospects. Current Opinion in Environmental Sustainability 5,667–675.
Poff, N. L., Olden, J. D., Merritt, D. M. & Pepin, D. M. (2007). Homogenizationof regional river dynamics by dams and global biodiversity implications. Proceedings
of the National Academy of Sciences of the United States of America 104, 5732–5737.Poff, N. L., Richter, B. D., Arthington, A. H., Bunn, S. E., Naiman, R.
J., Kendy, E., Acreman, M., Apse, C., Bledsoe, B. P., Freeman, M. C.,Henriksen, J., Jacobson, R. B., Kennen, J. G., Merritt, D. M., O’Keefe,J. H., Olden, J. D., Rogers, K., Tharme, R. E. & Warner, A. (2010). Theecological limits of hydrologic alteration (ELOHA): a new framework for developingregional environmental flow standards. Freshwater Biology 55, 147–170.
Poff, N. L. & Zimmerman, J. K. H. (2010). Ecological responses to altered flowregimes: a literature review to inform the science and management of environmentalflows. Freshwater Biology 55, 194–205.
*Pollock, M. M., Naiman, R. J. & Hanley, T. A. (1998). Plant species richness inriparian wetlands – a test of biodiversity theory. Ecology 79, 94–105.
Porst, G., Naughton, O., Gill, L., Johnston, P. & Irvine, K. (2012). Adaptation,phenology and disturbance of macroinvertebrates in temporary water bodies.Hydrobiologia 696, 47–62.
*Porter, J. L., Kingsford, R. T. & Brock, M. A. (2007). Seed banks in aridwetlands with contrasting flooding, salinity and turbidity regimes. Plant Ecology 188,215–234.
Procopio, N. A. (2012). The effect of streamflow reductions on aquatic habitatavailability and fish and macroinvertebrate assemblages in coastal plain streams.Ecohydrology 5, 306–315.
Puckridge, J. T., Costelloe, J. F. & Reid, J. R. W. (2010). Ecological responses tovariable water regimes in arid-zone wetlands: Coongie Lakes, Australia. Marine and
Freshwater Research 61, 832–841.Puckridge, J. T., Sheldon, F., Walker, K. F. & Boulton, A. J. (1998). Flow
variability and the ecology of large rivers. Marine and Freshwater Research 49, 55–72.Purvis, A. & Hector, A. (2000). Getting the measure of biodiversity. Nature 405,
212–219.Rahel, F. J. (2010). Homogenization, differentiation, and the widespread alteration
of fish faunas. In Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques
(eds K. B. Gido and D. A. Jackson), pp. 311–326. American Fisheries Society,Bethesda.
*Raulings, E. J., Morris, K., Roache, M. C. & Boon, P. I. (2010). The importanceof water regimes operating at small spatial scales for the diversity and structure ofwetland vegetation. Freshwater Biology 55, 701–715.
Resh, V. H., Brown, A. V., Covich, A. P., Gurtz, M. E., Li, H. W., Minshall,G. W., Reice, S. R., Sheldon, A. L., Wallace, J. B. & Wissmar, R. C. (1988).The role of disturbance in stream ecology. Journal of the North American Benthological
Society 7, 433–455.Reyers, B., Polasky, S., Tallis, H., Mooney, H. A. & Larigauderie, A. (2012).
Finding common ground for biodiversity and ecosystem services. Bioscience 62,503–507.
Riis, T. & Biggs, B. J. F. (2003). Hydrologic and hydraulic control of macrophyteestablishment and performance in streams. Limnology and Oceanography 48, 1488–1497.
Riis, T., Suren, A. M., Clausen, B. & Sand-Jensen, K. (2008). Vegetation and flowregime in lowland streams. Freshwater Biology 53, 1531–1543.
Robach, F., Eglin, I. & Tremolieres, M. (1997). Species richness of aquaticmacrophytes in former channels connected to a river: a comparison between twofluvial hydrosystems differing in their regime and regulation. Global Ecology and
Biogeography Letters 6(274), 267.
Robson, B. J., Hogan, M. & Forrester, T. (2005). Hierarchical patterns ofinvertebrate assemblage structure in stony upland streams change with time andflow permanence. Freshwater Biology 50, 944–953.
*Rodrigues, D. J., Lima, A. P., Magnusson, W. E. & Costa, F. R. C. (2010).Temporary pond availability and tadpole species composition in Central Amazonia.Herpetologica 66, 124–130.
Rooney, T. P., Olden, J. D., Leach, M. K. & Rogers, D. A. (2007). Biotichomogenization and conservation prioritization. Biological Conservation 134, 447–450.
Rose, P., Metzeling, L. & Catzikiris, S. (2008). Can macroinvertebrate rapidbioassessment methods be used to assess river health during drought in south easternAustralian streams? Freshwater Biology 53, 2626–2638.
Santos, A. N. & Stevenson, R. D. (2011). Comparison of macroinvertebratediversity and community structure among perennial and non-perennial headwaterstreams. Northeastern Naturalist 18, 7–26.
*Schalk, C. M., Montana, C. G., Winemiller, K. O. & Fitzgerald, L. A. (2017).Trophic plasticity, environmental gradients and food-web structure of tropical pondcommunities. Freshwater Biology 62, 519–529.
*Schneider, B., Cunha, E. R., Marchese, M. & Thomaz, S. M. (2015).Explanatory variables associated with diversity and composition of aquaticmacrophytes in a large subtropical river floodplain. Aquatic Botany 121, 67–75.
*Schoen, J., Merten, E. & Wellnitz, T. (2013). Current velocity as a factor indetermining macroinvertebrate assemblages on wood surfaces. Journal of Freshwater
Ecology 28, 271–275.*Schriever, T. A., Bogan, M. T., Boersma, K. S., Canedo-Arguelles, M.,
Jaeger, K. L., Olden, J. D. & Lytle, D. A. (2015). Hydrology shapes taxonomicand functional structure of desert stream invertebrate communities. Freshwater Science
34, 399–409.*Serrano, L. & Fahd, K. (2005). Zooplankton communities across a hydroperiod
gradient of temporary ponds in the Donana National Park (SW Spain). Wetlands 25,101–111.
Sheldon, F., Boulton, A. J. & Puckridge, J. T. (2002). Conservation value ofvariable connectivity: aquatic invertebrate assemblages of channel and floodplainhabitats of a central Australian arid-zone river, Cooper Creek. Biological Conservation
103, 13–31.Silver, C. A., Vamosi, S. M. & Bayley, S. E. (2012). Temporary and permanent
wetland macroinvertebrate communities: phylogenetic structure through time. Acta
Oecologica-International Journal of Ecology 39, 1–10.Sim, L. L., Davis, J. A., Strehlow, K., Mcguire, M., Trayler, K. M., Wild, S.,
Papas, P. J. & O’Connor, J. (2013). The influence of changing hydroregime onthe invertebrate communities of temporary seasonal wetlands. Freshwater Science 32,327–342.
*Spencer, B., Schwartz, S. S. & Cohen, J. E. (1999). Species richness and theproportion of predatory animal species in temporary freshwater pools: relationshipswith habitat size and permanence. Ecology Letters 2, 157–166.
Sponseller, R. A., Heffernan, J. B. & Fisher, S. G. (2013). On the multipleecological roles of water in river networks. Ecosphere 4, 17.
Starr, S. M., Benstead, J. P. & Sponseller, R. A. (2014). Spatial and temporalorganization of macroinvertebrate assemblages in a lowland floodplain ecosystem.Landscape Ecology 29, 1017–1031.
Sternberg, D. & Kennard, M. J. (2013). Environmental, spatial and phylogeneticdeterminants of fish life-history traits and functional composition of Australian rivers.Freshwater Biology 58, 1767–1778.
*Storey, R. (2016). Macroinvertebrate community responses to duration, intensityand timing of annual dry events in intermittent forested and pasture streams. Aquatic
Sciences 78, 395–414.Strayer, D. L. & Dudgeon, D. (2010). Freshwater biodiversity conservation: recent
progress and future challenges. Journal of the North American Benthological Society 29,344–358.
Strecker, A. L., Olden, J. D., Whittier, J. B. & Paukert, C. P. (2011). Definingconservation priorities for freshwater fishes according to taxonomic, functional, andphylogenetic diversity. Ecological Applications 21, 3002–3013.
Stromberg, J. C., Bagstad, K. J., Leenhouts, J., Lite, S. J. & Making, S. E.(2005). Effects of stream flow intermittency on riparian vegetation of a semiaridregion river (San Pedro River, Arizona). River Research and Applications 21, 925–938.
Stromberg, J. C., Hazelton, A., White, M., White, J. & Fischer, R. (2009).Ephemeral wetlands along a spatially intermittent river: temporal patterns ofvegetation development. Wetlands 29, 330–342.
Stubbington, R., Boulton, A. J., Little, S. & Wood, P. J. (2015). Changesin invertebrate assemblage composition in benthic and hyporheic zones during asevere supraseasonal drought. Freshwater Science 34, 344–354.
*Sullivan, S. M. P. & Watzin, M. C. (2009). Stream-floodplain connectivity andfish assemblage diversity in the Champlain Valley, Vermont, U.S.A. Journal of Fish
Biology 74, 1394–1418.Svec, J. R., Kolka, R. K. & Stringer, J. W. (2005). Defining perennial,
intermittent, and ephemeral channels in Eastern Kentucky: applicationto forestry best management practices. Forest Ecology and Management 214,170–182.
Swenson, N. G. (2011). The role of evolutionary processes in producing biodiversitypatterns, and the interrelationships between taxonomic, functional and phylogeneticbiodiversity. American Journal of Botany 98, 472–480.
Swirepik, J. L., Burns, I. C., Dyer, F. J., Neave, I. A., O’Brien, M. G., Pryde, G.M. & Thompson, R. M. (2016). Establishing environmental water requirements forthe Murray–Darling Basin, Australia’s largest developed river system. River Research
and Applications 32, 1153–1165.Tedesco, P. A., Hugueny, B., Oberdorff, T., Durr, H. H., Merigoux, S. & De
Merona, B. (2008). River hydrological seasonality influences life history strategiesof tropical riverine fishes. Oecologia 156, 691–702.
Thomaz, S., Bini, L. & Bozelli, R. (2007). Floods increase similarity among aquatichabitats in river-floodplain systems. Hydrobiologia 579, 1–13.
Thoms, M. C. & Parsons, M. (2003). Identifying spatial and temporal patternsin the hydrological character of the Condamine-Balonne river, Australia, usingmultivariate statistics. River Research and Applications 19, 443–457.
Timoner, X., Acuna, V., Frampton, L., Pollard, P., Sabater, S. & Bunn, S. E.(2014). Biofilm functional responses to the rehydration of a dry intermittent stream.Hydrobiologia 727, 185–195.
Tobias, N. & Monika, W. (2012). Does taxonomic homogenization imply functionalhomogenization in temperate forest herb layer communities? Plant Ecology 213,431–443.
Tornes, E. & Ruhí, A. (2013). Flow intermittency decreases nestedness andspecialisation of diatom communities in Mediterranean rivers. Freshwater Biology
58, 2555–2566.Tornwall, B., Sokol, E., Skelton, J. & Brown, B. (2015). Trends in stream
biodiversity research since the river continuum concept. Diversity 7, 16–35.Townsend, C. R., Scarsbrook, M. R. & Doledec, S. (1997). The intermediate
disturbance hypothesis, refugia, and biodiversity in streams. Limnology and Oceanography
42, 938–949.Trentanovi, G., Von Der Lippe, M., Sitzia, T., Ziechmann, U., Kowarik, I. &
Cierjacks, A. (2013). Biotic homogenization at the community scale: disentanglingthe roles of urbanization and plant invasion. Diversity and Distributions 19, 738–748.
Tucker, C. M., Cadotte, M. W., Carvalho, S. B., Davies, T. J., Ferrier, S.,Fritz, S. A., Grenyer, R., Helmus, M. R., Jin, L. S., Mooers, A. O., Pavoine,S., Purschke, O., Redding, D. W., Rosauer, D. F., Winter, M. & Mazel, F.(2017). A guide to phylogenetic metrics for conservation, community ecology andmacroecology. Biological Reviews 92, 698–715.
Turak, E., Harrison, I., Dudgeon, D., Abell, R., Bush, A., Darwall, W.,Finlayson, C. M., Ferrier, S., Freyhof, J., Hermoso, V., Juffe-Bignoli, D.,Linke, S., Nel, J., Patricio, H. C., Pittock, J., Raghavan, R., Revenga,C., Simaika, J. P. & De Wever, A. (2017). Essential Biodiversity Variablesfor measuring change in global freshwater biodiversity. Biological Conservation 213,272–279.
Uchida, Y. & Inoue, M. (2010). Fish species richness in spring-fed ponds: effects ofhabitat size versus isolation in temporally variable environments. Freshwater Biology
55, 983–994.*Urban, M. C. (2004). Disturbance heterogeneity determines freshwater
metacommunity structure. Ecology 85, 2971–2978.Van Den Brink, F. W. B., Van Der Velde, G., Buijse, A. D. & Klink, A. G.
(1996). Biodiversity in the lower Rhine and Meuse river-floodplains: its significancefor ecological river management. Netherland Journal of Aquatic Ecology 30, 129–149.
Van Der Nat, D., Schmidt, P. A., Tockner, K., Edwards, J. P. & Ward, V. J.(2002). Inundation dynamics in braided floodplains: tagliamento River, northeastItaly. Ecosystems 5, 0636–0647.
Van Grunsven, R. H. A. & Liefting, M. (2015). How to maintain ecologicalrelevance in ecology. Trends in Ecology & Evolution 30, 563–564.
*Van Looy, K., Piffady, J. & Floury, M. (2017). At what scale and extentenvironmental gradients and climatic changes influence stream invertebratecommunities? Science of the Total Environment 580, 34–42.
*Vanschoenwinkel, B., De Vries, C., Seaman, M. & Brendonck, L. (2007). Therole of metacommunity processes in shaping invertebrate rock pool communitiesalong a dispersal gradient. Oikos 116, 1255–1266.
Villeger, S., Blanchet, S., Beauchard, O., Oberdorff, T. & Brosse, S. (2011).Homogenization patterns of the world’s freshwater fish faunas. Proceedings of the
National Academy of Sciences of the United States of America 108, 18003–18008.Villeger, S., Grenouillet, G. & Brosse, S. (2013). Decomposing functional
β-diversity reveals that low functional β-diversity is driven by low functionalturnover in European fish assemblages. Global Ecology and Biogeography 22,671–681.
*Vinson, M. R. & Hawkins, C. P. (2003). Broad-scale geographical patterns in localstream insect genera richness. Ecography 26, 751–767.
Vorosmarty, C. J., Mcintyre, P. B., Gessner, M. O., Dudgeon, D., Prusevich,A., Green, P., Glidden, S., Bunn, S. E., Sullivan, C. A., Liermann, C. R. &
Davies, P. M. (2010). Global threats to human water security and river biodiversity.Nature 467, 555–561.
Walker, K. F., Sheldon, F. & Puckridge, J. T. (1995). A perspective on drylandriver ecosystems. Regulated Rivers: Research and Management 11, 85–104.
Ward, D. P., Hamilton, S. K., Jardine, T. D., Pettit, N. E., Tews, E. K.,Olley, J. M. & Bunn, S. E. (2013). Assessing the seasonal dynamics of inundation,turbidity, and aquatic vegetation in the Australian wet–dry tropics using opticalremote sensing. Ecohydrology 6, 312–323.
Ward, J. V. (1989). The four-dimensional nature of lotic ecosystems. Journal of the North
American Benthological Society 8, 2–8.Ward, J. V. & Tockner, K. (2001). Biodiversity: towards a unifying theme for river
ecology. Freshwater Biology 46, 807–819.Ward, J. V., Tockner, K. & Schiemer, F. (1999). Biodiversity of floodplain river
ecosystems: ecotones and connectivity1. Regulated Rivers: Research & Management 15,125–139.
Warfe, D. M., Hardie, S. A., Uytendaal, A. R., Bobbi, C. J. & Barmuta, L. A.(2014). The ecology of rivers with contrasting flow regimes: identifying indicators forsetting environmental flows. Freshwater Biology 59, 2064–2080.
Warren, S. D., Holbrook, S. W., Dale, D. A., Whelan, N. L., Elyn, M., Grimm,W. & Jentsch, A. (2007). Biodiversity and the heterogeneous disturbance regimeon military training lands. Restoration Ecology 15, 606–612.
*Webb, E. B., Smith, L. M., Vrtiska, M. P. & Lagrange, T. G. (2010). Effects oflocal and landscape variables on wetland bird habitat use during migration throughthe rainwater basin. Journal of Wildlife Management 74, 109–119.
*Werner, E. E., Skelly, D. K., Relyea, R. A. & Yurewicz, K. L. (2007). Amphibianspecies richness across environmental gradients. Oikos 116, 1697–1712.
Westgate, M. J., Barton, P. S., Lane, P. W. & Lindenmayer, D. B. (2014). Globalmeta-analysis reveals low consistency of biodiversity congruence relationships. Nature
Communications 5, 3899.Whittaker, R. H. (1960). Vegetation of the Siskiyou Mountains, Oregon and
California. Ecological Monographs 30, 279–338.Whittaker, R. J., Willis, K. J. & Field, R. (2001). Scale and species richness:
towards a general, hierarchical theory of species diversity. Journal of Biogeography 28,453–470.
Wiens, J. A. (1989). Spatial scaling in ecology. Functional Ecology 3, 385–397.Wiens, J. J. (2015). Faster diversification on land than sea helps explain global
biodiversity patterns among habitats and animal phyla. Ecology Letters 18, 1234–1241.*Wintle, B. C. & Kirkpatrick, J. B. (2007). The response of riparian vegetation to
flood-maintained habitat heterogeneity. Austral Ecology 32, 592–599.*Wissinger, S. A., Greig, H. & McIntosh, A. (2009). Absence of species
replacements between permanent and temporary lentic communities in NewZealand. Journal of the North American Benthological Society 28, 12–23.
*Wood, P. J., Gunn, J., Smith, H. & Abas-Kutty, A. (2005). Flow permanence andmacroinvertebrate community diversity within groundwater dominated headwaterstreams and springs. Hydrobiologia 545, 55–64.
Xenopoulos, M. A. & Lodge, D. M. (2006). Going with the flow: usingspecies-discharge relationships to forecast losses in fish biodiversity. Ecology 87,1907–1914.
Xenopoulos, M. A., Lodge, D. M., Alcamo, J., Marker, M., Schulze, K. &Vuuren, D. P. V. (2005). Scenarios of freshwater fish extinctions from climatechange and water withdrawal. Global Change Biology 11, 1557–1564.
Yang, W., Sun, T. & Yang, Z. (2016). Does the implementation of environmentalflows improve wetland ecosystem services and biodiversity? A literature review.Restoration Ecology 24, 731–742.
*Zilli, F. L. & Marchese, M. R. (2011). Patterns in macroinvertebrate assemblages atdifferent spatial scales. Implications of hydrological connectivity in a large floodplainriver. Hydrobiologia 663, 245–257.
*Zdot;mihorski, M., Part, T., Gustafson, T. & Berg, A. (2016). Effects of waterlevel and grassland management on alpha and beta diversity of birds in restoredwetlands. Journal of Applied Ecology 53, 587–595.
XI. SUPPORTING INFORMATION
Additional supporting information may be found in theonline version of this article.Appendix S1. Details of literature searches.Table S1. Summary of studies reporting relationshipsbetween ecohydrological mechanisms and river–floodplainbiodiversity across spatial scales sourced from Web of Science.
(Received 24 November 2016; revised 24 September 2017; accepted 2 October 2017; published online 8 November 2017)
